IMMUNO ORALS
1. Cells Involved in the Immune Response: Lymphoid Cells; Mononuclear Phagocytes
There are mainly 2 types of immunity adaptive(lymphocytes) and innate(macro, mono, nk, mast, granulocytes)
There are many cells involved in the immune responseLymphoid cells include b, nk(large granular lymphocytes) and t cells. Phagocytotic cells include Mononuclear
phagocytes(macro, mono) and Polymorphonuclear phagocytes (granulocutes)
Cell-mediated arm consists of T lymphocytes (e.g., helper T cells and cytotoxic T cells)
Antibody-mediated arm consists of antibodies (immunoglobulins) and B lymphocytes (and plasma cells)
T cells- They have T cell antigen receptor. They arise from Thymus. Diff types Th helps and induces immune responses,
Tcyt destroys virus infected cells and tumour cells, Treg regulates immune responces, Tmem augmented immune
response after reintroduction of pathogen.
T helper cells can be further divided into Th1 sec IL2 and IFNgamma, Th2 sec IL4-5-6-10.
B cells- B cells develop mainly in the fetal liver and bone marrow. Most b cells in blood expresses IgM and IgD i sotypes.
Other immunoglobulin isotypes may be expressed at particular sites. Other B cell markers include MHC class 2 antigens
and complement and Fc receptors. Following B cell activation, B cells mature into AFC which progress to form Plasma
cells. Plasma cells secrete antibodies.
NK cells- Natural killer (NK) cells are effector lymphocytes of the innate immune system that control several types of
tumors and microbial infections by limiting their spread and subsequent tissue damage. CD16(immature) and
CD64(mature) are important markers for NK cells.
Monocytes/Macr
ophages- Monocytes (Mo) circulating blood cells and macrophages (Mϕ) differentiated from monocytes and residing in
various tissues are key components of the innate immune system and are involved in regulation of the initiation,
development, and resolution of many inflammatory disorders.
Monocyte and Macrophages actively phagocyte organisms and bodys own cells and tumour cells. Phagocytosis can be
enhanced by opsonisation. Granulocytes and monocytes have the same progenitor origin, they arise from the myeloid
lineage. Monocytes express CD14 and significant levels of MHC class 2 molecules.
Mono nuclear phagocytes are cells that work for phagocytosis.
1) Kupffer cells- macrophages of the liver, comprise the largest pool of tissue macrophages in the body
2) Microglia- the central nervous system (CNS). They remove damaged neurons and infections and are important for
maintaining the health of the CNS.
3) Osteo-clasts- bone- degrade bone to initiate normal bone remodeling and mediate bone loss in pathologic conditions
by increasing their resorptive activity.
2. Cells involved in the immune response: antigen-presenting cells; polymorphs, mast cell and platelets
Antigen- presenting cells a heterogeneous group of immune cells that mediate the cellular immune response by
processing and presenting antigens for recognition by certain lymphocytes such as T cells. Proffesional APCs include
dendritic cells,
macrophages,
Langerhans cells and
B cells.
Non Professional APC’s include Fibroblasts, glial cells, pancreatic B cells, Thymic epithelial cells etc
Macrophages have 3 main functions- phagocytosis, antigen presentation and cytokine production.
Steps1234-
Foreign material is ingested and degraded
fragments of antigen are presented on the macrophage cell surface (in conjunction with class II MHC proteins)
for interaction with the TCR of CD4-positive helper T cells.
Degradation of the foreign protein stops when the fragment associates with the class II MHC protein in the
cytoplasm. The complex is then transported to the cell surface by specialized “transporter” proteins.
Dendritic Cells
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function as “professional” APCs,
they are the main inducers of the primary antibody response
name dendritic describes their many long, narrow processes (resembling neuronal dendrites), which make them
very efficient at making contact with foreign material.
primarily located under the skin and the mucosa
migrate from their peripheral location under the skin and mucosa to local lymph nodes where they present
antigen to helper T cells
migration of dendritic cells to the lymph nodes is a response to the chemokine, CCR7, produced by T cells in the
lymph nodes.
Langerhan cells
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Langerhans cells (LC) are a unique population of tissue-resident macrophages that form a network of cells across
the epidermis of the skin, but which have the ability to migrate from the epidermis to draining lymph
nodes (LN).
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In lymph nodes they interact with T cells and are termed interdigitating cells.
Polymorphs
There are three different types, Neutrophils, Eosinophils and Basophils. The polymorphonuclear granulocytes (often
referred to as polymorphs or granulocytes) consist mainly of neutrophils (PMNs).
Neutrophils- Neutrophils are a type of white blood cell (leukocytes) that act as your immune system's first line of
defense. They have the same progenitor cells as Monocytes and they arise from the myeloid lineage. They have
Granules containing lysozymes, acid hydrolases, peroxidases etc. They express adhesion molecules CD11 abc and CD 18
and receptors involved in phagocytosis FcgRIII,II,I.
Eosinophils- Eosinophils are thought to play a role in immunity to parasitic worms. Eosinophils comprise 2–5% of blood
leukocytes in healthy, non-allergic individuals. Human blood eosinophils usually have a bilobed nucleus and many
cytoplasmic granules, which stain with acidic dyes such as eosin. Although not their primary function, eosinophils appear
to be capable of phagocytosing and killing ingested microorganisms.
Basophils- Basophils along with Mast cells play an imp role in allergic reactions. Allergens stimulates an IgE bound
molecule of bp to promote degranulation and release of histamine cause adverse symptoms of allergy.
Mast cells
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are similar to basophils in many ways
fixed in tissue, especially under the skin and in the mucosa of the respiratory and GI tracts.
have receptors on the cell surface for the Fc portion of the heavy chain of IgE.
When adjacent IgE molecules are cross-linked by antigen, immunologically active mediators, such as histamine,
peroxidases and hydrolases, are released. These cause inflammation and, when produced in large amounts,
cause severe immediate hypersensitivity reactions such as systemic anaphylaxis.
also play an important role in the innate response to bacteria and viruses.
surface of mast cells contains Toll-like receptors that recognize bacteria and viruses.
The mast cells respond by releasing cytokines and enzymes from their granules that mediate inflammation and
attract neutrophils and dendritic cells to the site of infection. Dendritic cells are important APCs that initiate
the adaptive response. The role of mast cells in inflammation has been demonstrated in rheumatoid arthritis.
These cells produce both inflammatory cytokines and the enzymes that degrade the cartilage in the joints.
Platelets (coagulation)
Aka thrombocytes (thrombus- clot, cytes- cells)
Decreased number of platelets- Thrombocytopenia
Increased number of cells- thrombocytosis or Thrombocythemia
Synthesized from megakaryocytes
Megakaryocytes are made in the bone marrow and while leaving they squeeze through the capillaries and breakdown
and thousands of pieces of these are called platelets
Platelets do not have nucleus and cannot divide because they are pieces of megakaryocytes.
On bone marrow biopsies- we do not see platelets, we only see megakaryocytes
Where do we find platelets?
1. Peripheral blood
2. Spleen – that’s why splenomegaly decreases the platelet count. Thrombocytopnia can be treated by removing
the spleen
What stimulates platelet production
1. thrombopoieten
2. IL-6
Platelets are removed by splenic macrophages
And are regenerated by the bone marrow (by megakaryocytes)
Structure of PlateletsBiconvex
Plasma membrane
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Has glycoproteins coat- Receptors- GPIb and GP2b/3a
Mode of lipids (including phospholipids) (arachiadonic acid)
Ca2+ canaciluar system
Cytoplasm
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Actin and myosin
Thrombostenin
Residuals of golgi and RER (for enzyme synthesus)
Fibrin stabilizing factor
Platelet derived growth factor (help repair the vessel after thrombus)
Platelet granules are two kinds1. Alpha
Protein, strong
Include- Factor XIII
PAF
PDGF
vWF
Fibrinogen
PF4 (platelet factor 4)
2. Dense
Non-protein
IncludeADP
Ca2+ (for contraction and binding agents vitamin K dependent factors)
Normal platelet count- 150,000-400,000 per microliter
3. Primary lymphoid organs
Thymus and Bone marrow
Thymus- Produces T-cells
Larger at birth and reduces in size with age.
The thymus in mammals is a bilobed organs in the thoracic cavity overlying the heart and major blood vessels.
Each lobe is organized into lobules separated from each other by connective tissue trabeculae.
Within each lobule, the lymphoid cells (thymocytes) are arranged into-
1. An outer packed cortex
2. An inner medulla
Steps of formation of T cells1. Stem cell migration- initiates t cell development
2. Mature T cells leave the thymus via HEVs at the corticomedullary junction
3. Positive and Negative selection of developing T-cells that takes place in the thymus
Positive selection- Only those TCRs with an immediate affinity for self MHC are allowed to develop further.
Negative selection- some of the positively selected cells may have T cells that recognize self-components other than
self-MHC. So these cells are removed by a negative selection process which is
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In cortex,
Coticomedullary junction and
Medulla.
Negative selection may also occur outside the thymus in the peripheral lymphoid tissues.
Bone marrow- Produces B-cells
In the bone marrow, the B cells mature in close association with stromal reticular cells.
(Bone marrow is both a primary and a secondary lymphoid organ because it produces both B cells and NK cells)
4. Secondary lymphoid organs
Cellular and humoral immunity occurs in the secondary lymphoid organsSpleen
The spleen is made up of white pulp, red pulp, and a marginal zone.The spleen lies at the upper left quadrant of the
abdomen, behind the stomach and close to the diaphragm. The outer layer of the spleen consists of a capsule of
collagenous bundles of fibers, which enter the parenchyma of the organ as short trabeculae.
These, together with a reticular framework, support two main types of splenic tissue:
• the white pulp- The white pulp of the spleen consists of lymphoid tissue, the bulk of which is arranged around a
central arteriole to form the periarteriolar lymphoid sheaths (PALS). PALS are composed of T and B cell areas.
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the red pulp- The red pulp consists of venous sinuses and cellular cords.
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the marginal zone, is located at the outer limit of the white pulp, contains B cells, macrophages, and dendritic
cells.
Lymph-nodesSmall solid structures located at different points along the lymphatic system. They trap the microorganisms or other
antigens which get into the lymph and tissue fluid. Lymph nodes filter antigens from the interstitial tissue fluid and
lymph. Lymph nodes consist of B and T cell areas and a medulla. A typical lymph node is surrounded by a collagenous
capsule. Radial trabeculae, together with reticular fibers, support the various cellular components.
The lymph node consists of:
• a B cell area (cortex);
• a T cell area (paracortex); and `
• a central medulla, consisting of cellular cords containing T cells, B cells, abundant plasma cells, and macrophages
Tonsils- The tonsils contain a considerable amount of lymphoid tissue, often with large secondary follicles and
intervening T cell zones with HEVs
Peyers patch of small intestine (Ileum)
MALT- mucosa-associated lymphoid tissue- Constitutes 50% of the lymphoid tissue of human body.
Located within the lining of the major tracts as respiratory, digestive and urogenital tract.
5. Lymphocyte traffic
T-lymphocytes leave the bloodstream across the specialized endothelial walls of the blood vessels called high
endothelial venules (HEV)
The continuous process of circulation and recirculation of lymphocyte through blood and lymph is refereed to as
lymphocyte traffic.
The lymphocyte that enter the blood from the primary lymphoid circulate through the secondary lymphoid organs and
circulate back to the blood via the lymphatic system to be recirculated in the very same pathway.
B-cells have a limited capacity to circulate.
Functions of lymphocyte traffica) Helps the antigen presenting cells to carry out surveillance work by wandering through the body.
b) Helps the army of immune cells to march to the site of the infection.
c) The naïve immune cells are exposed to the pathogens.
6. Activation of complement: the classical pathway
Several complement components are proenzymes (they have to be cleaved to be activated)
Complement activation can occur through 3 pathways- Classic, lectin and alternative pathways.
Complement proteins are from C1 to C9
Antibodies (classical pathway) and factors B,D, P (alternative pathways)
The proteins are activated cleaved into a and b fragments. A is often the smaller and inactive while b is larger and active.
But c2a is active and larger but C2b is inactive and smaller.
Classical Pathway
Antibody dependent pathway
The antibody attaches to the microbe giving antigen-antibody complex.
C1 protein complex binds to antigen-antibody (antibodies here are IgG and IgM)
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C4 is cleaved to C4a and C4b
C2 is cleaved to C2a and C2b
C4b+C2a= C4b2a aka C3-convertase
C3 convertase converts C3 into C3a and c3b
C3a works in inflammation
C3b attaches to C4b2a -called C4b2a3b (=C5 convertase)
C5 convertase converts C5 into C5a and C5b
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C5b recruits C6 and C7
We get C5b, 6,7
C8 is recruited
We get C5b6,7,8
We get poly C9- called Mac (Membrane attack complex- forms pores)
C3b—opsonization.
C3a, C4a, C5a—anaphylaxis.
C5a—neutrophil chemotaxis.
7. Activation of complement; the alternative pathway
Alternative pathway
Antibody-independent
We need 3 components1. Factor B- activator of fluid phase C3-convertase
2. Factor D- Cleaves factor B
3. Properdin Protein (P)- Helps in attacking C3b molecule towards cell membrane of pathogens.
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C3 molecule is present in plasma undergoes spontaneous hydrolysis and becomes C3 (H2O)
Factor B in plasma is converted to Bb and Ba by Factor D
Bb combines with C3(H2O) and we get C3 (H2O)Bb also called fluid phase C3 convertase.
Fluid phase C3 convertase changes C3 to C3a and C3b
C3bBb- stable convertase that changes C3 to C3a and C3b
Propidin molecule adds to this and makes C3bBb3b--- C5 convertase
C5 convertase cleaves C5 to C5a and C5b
8. Biological effect of compliment
The three main consequences of complement activation are
1- opsonization of pathogens,
2- the recruitment of inflammatory cells, and
3- direct killing of pathogens
Opsonization is the important process in host defense by which particles or complexes are made readily ingestible for
uptake by phagocytic cells. Specific serum proteins, known as opsonins, coat particles and cause the particles to bind
avidly to phagocytes and trigger ingestion.
Role of lymphocte in adaptive immunity
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Immature B cells bind directly to foreign particles and mature through positive selection
Mature cells encounter with opsonized antigens leading to activation and proliferation
Follicular dendritic cells capture antigen throough attached C3 fragments
Activates specific B cells
Further maturation and proliferation
Differentiates into plasma and memory B cells
Classical pathway deficiencies lead to SLE, necrosis, skin lesions and kidney damage.
Alternative pathway deficiencies Renal failure, meningitis etc.
9. Cell migration and inflammation
Inflammation is of two types- acute and chronic
Acute inflammation has 2 outcomes- complete resolution or further proceeds to chronic inflammation
Chronic inflammation has 2 outcomes- complete resolution or reparation.
Reparation is the substitution of the damaged cells by connective tissue cells.
There’s also so regeneration which happens in liver.
Mechanism1. Margination and rolling by E-selectin, P-selectin and Glycan CD34
2. Adhesion by integrins
3. Diapstesis and transmigration by PECAM.
10. Immunoglobulins. Antibody structure
Immunoglobulins are mainly produced from B lymphocytes. They are of multi-domain architecture that helps in
recognition and binding to foreign molecules and lead to their sequestration.
Structure of Antibody
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A Y shaped structure
2 Heavy and 2 Light chains
Variable, constant and hinge regions
Disulphide bonds present in between.
ImmunoglobulinsIgA- Mostly seen in mucosal secretions (colostrum, tears etc), dimeric in nature
IgM- Monomeric or pentameric, often the first immunoglobulins elicited when a foreign substance is noticed, found only
in plasma
IgG- Monomeric, High concentration in plasma, takes longer to be produced (10 days). Only Ig that can cross the
placenta.
IgD- Only on B lymphocytes.
IgE- In response to allergens. Eg- Anaphylactic shock, asthama and hay fever.
The most important functions of antibodies are to
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neutralize toxins and viruses,
to opsonize microbes so they are more easily phagocytosed,
to activate complement, and
to prevent the attachment of microbes to mucosal surfaces.
11. Antibody receptors. Antibody structure and function
FcR receptors act on the constant region of heavy chains in antibodies
1. IgG- FcrRI, FcrRII, FcrRIII
2. IgA- FcalphaRI- expressed in myeloid cells and triggers phagocytosis, cell lysis and release of inflammatory
mediators.
3. IgE- FcERI, FcERII- expressed in mast cells, basophils and leukocytes.
12. T-cell receptors
We can divide immune system of higher vertebrates into two components- Humoral immunity and cell mediated
immunity. Humoral immunity provides protection via extracellular fluid and thus we need a back up which can come
into effect when humoral imm fails and that is given by the cell mediated immunity of which t cells are a huge part
of.
T cells recognize antigen via T cell receptors through V(D)J recombination in variable regions.
TCRs can only engage when cells are interacting close to each other due to MHC molecules only being present on cell
surfaces. The requirement of cell cell interaction also shows T cells to provide critical regulatory functions. Adaptive
immunity is being coupled with innate immunity.
T-cell receptors consist of two polypeptide chains. The most common type of receptor is called alpha-beta because it is
composed of two different chains, one called alpha and the other beta. The regions of greatest variability correspond to
immunoglobulin hypervariable regions and are also known as complementarity determining regions (CDRs). They are
clustered together to form an antigen-binding site analogous to the corresponding site on antibodies. The CD3 complex
associates with the antigenbinding ab or gd heterodimers to form the complete TCR. The four members of the CD3
complex (g, d, e, and z) are sometimes termed the invariant chains of the TCR because they do not show variability in
their amino acid sequences. The cytoplasmic portions of z and chains contain ITAMs. The cytoplasmic portions of these
subunits contain particular amino acid sequences called immunoreceptor tyrosine-based activation motifs (ITAMs), and
each chain contains three of these motifs.
A less common type is the gamma-delta receptor, which contains a different set of chains, one gamma and one delta.
The gd TCR structurally resembles the ab TCR but may function differently
13. Major histocompatibility complex(MHC) antigens
Major histocompatibility complex (MHC) is the cluster of gene arranged within a long continuous stretch of DNA on
chromosome number 6 in Human which encodes MHC molecules. They are also called HLA (human leukocyte Antigen)
molecules.
MHC class I molecules handle endogenous (or intrinsic) antigens, while MHC class II molecules handle exogenous
(extrinsic) antigens. In both cases, the antigenic peptides are produced by proteolytic processing of proteins.
In general:
• MHC class I molecules present antigen to cytotoxic T cells, which are important in controlling viral infections by lysing
infected cells;
• MHC class II molecules present antigen to helper T cells, which aid B cells in generating antibody responses to
extracellular protein antigens.
There are 3 classes of MHC-
1. MHC Class IRegions- A,B,C
Gene products- HLA-A, HLA-B, HLA-C
2. MHC Classs II
Regions- DP, DQ, DR
3. MHC Class III
Regions- C4, C2, BF
Gene products- C’ Protein, TNF-alpha, TNF-beta
14. Genomic organization of MHC
The human MHC class I region contains three principal class I loci – called HLA-A, HLA-B, and HLA-C.
The HLA-E, HLA-F, HLA-G, and HLA-H genes also encode MHC class I proteins, and are called class Ib genes. They
are much less polymorphic than the A, B, and C locus gene products, and recent work has ascribed various
functions to them.
Human MHC class II genes are located in the HLA-D region
Three loci (DR, DQ, and DP) encode the major expressed products of the human MHC class II region.
15. Immunoglobulin variability. Immunoglobulin gene recombination. Somatic mutation
somatic mutation, genetic alteration acquired by a cell that can be passed to the progeny of the mutated cell in the
course of cell division. Somatic mutations differ from germ line mutations, which are inherited genetic alterations that
occur in the germ cells
16. Cytokines and their receptors. T-cell independent defense mechanisms
Cytokines are small soluble factors with pleiotropic functions that are produced by many cell types as part of a gene
expression pattern that can influence and regulate the function of the immune system.
Cytokines
1. TNF- produced by T lymphocytes
2. IL-2 -T lymphocytes mast cells epithelial cells
Important roles of cytokines1. Endothelial activation
2. Activation of leukocytes and other cells
3. Systemic acute phase response
T-cell independent defense mechanisms
Key players1.
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Macrophages
Phagocytes
NK cells
Eosinophils
Mast cells and basophils
17. Antigen presentation to T-cell. B-Cell-T-cells interaction
Endogenous peptides present antigen on MHC class I molecules to CD8 T cells
Exogenous peptides present antigen to MHC class II on Cd4 T cells
Dendritic cells, macrophages and B cells present antigen to T cells
Interaction between T cell and APC- T cells initially encounter with APCs via non-specificbinding through adhesion
molecules (ICAM and LFA-1)
T cells links with appropriate peptide/MHC molecule ---cuases conformational change in LFA1 (signaled via TCr) --Results in tight binding to ICAM 1 and prolonged cell-cell communication; APC and T cells dissociate---activated T cell
undergoes several rounds of division and degradation.
Process of interaction between B cells and T cells
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CD40 sends an activating signal to B cells
T cells expresses CD40L ligand which interacts with CD40
Drives B cells into cell cycle
Signal transduction through CD40 induces upregulation of CD80/CD86
Provides more costimulatory signals to responding T cells
18. Intracellular signaling events in lymphocyte activation. Cytokine actions on B-cells and T-cells. Antibody
responses in vivo
B cell activation
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Membrane immunoglobulin becomes cross linked with T dependent antigen
Tyrosine kinase is activated
ITAM domains get phosphorylated in Ig alpha and Ig beta chains
Bind to Syk kinase
Phospholipase C activation
Acts on membrane PIP2
Generates IP3 and diacyl glycerol (DAG)
Activates protein kinase C
Lymphocyte activation
Process is controlled by coreceptor complexes CD21, CD19, CD81
Cytokines produced by T helper cells promotes activation of B cells along woth production of IgG1 and IgE
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IL-4 acts on b cells and induces activation and differentiation
IL-5 growth and activation factor for eosinophils
IL-6 produced by T cells, macrophages and B cells
IL-10 growth and differentiation factor for B cells, modulates cytokine production of TH1 cells
19. Development of immune system. Positive and negative selection
Lymphoid stem cells develop and mature within primary lymphoid organs
In mammals, T cells mature in the thymus and B cells mature in the fetal liver and postnatal bone marrow
Tcells develop in thymus- Three types of thymic epithelial cell have important roles in T cell production.
At least three types of epithelial cell can be distinguished in the thymic lobules according to distribution, structure,
function, and phenotype:
• the epithelial nurse cells are in the outer cortex;
• the cortical thymic epithelial cells (TECs) form an epithelial network; and
• the medullary TECs are mostly organized into clusters
These three types of epithelial cell have different roles for thymocyte proliferation, maturation, and selection:
• nurse cells in the outer cortex sustain the proliferation of progenitor T cells, mainly through cytokine production (e.g.
IL-7);
• cortical TECs are responsible for the positive selection of maturing thymocytes, allowing survival of cells that recognize
MHC class I and II molecules with associated peptides via TCRs of intermediate affinity; and
• medullary TECs display a large variety of organ-specific self peptides through transcription factors such as AIRE
(autoimmune regulator).
B cells develop in fetal liver and bone marrow- The site of B cell production moves from the liver to the bone marrow,
where it continues through adult life. In the bone marrow, B cells mature in close association with stromal reticular cells,
which are found both adjacent to the endosteum and in close association with the central sinus, where they are termed
adventitial reticular cells.
Most B cells (>75%) maturing in the bone marrow do not reach the circulation, but (like thymocytes) undergo a process
of programmed cell death (apoptosis) and are phagocytosed by bone marrow macrophages.
Many self-reactive B cells are also eliminated through negative selection in the bone marrow.
Positive selection- (the first stage of thymic education) ensures that only those TCRs with an intermediate affinity for self
MHC are allowed to develop further. T cells displaying very high or very low receptor affinities for self MHC undergo
apoptosis and die in the cortex. T cells with TCRs that have intermediate affinities are rescued from apoptosis, survive,
and continue along their pathway of maturation.
Negative selection- Ensures that only T cells that fail to recognize self antigen proceed in their development. Some of
the positively selected T cells may have TCRs that recognize self components other than self MHC.
These cells are deleted by a ‘negative selection’ process, which occurs:
• in the deeper cortex;
• at the corticomedullary junction; and
• in the medulla.
Only T cells that fail to recognize self antigen are allowed to proceed in their development. The rest undergo apoptosis
and are destroyed.
Tissue-restricted self-antigens are expressed in the thymus due to the action of autoimmune regulator (AIRE); deficiency
leads to autoimmune polyendocrine syndrome-1
(Chronic mucocutaneous candidiasis, Hypoparathyroidism, Adrenal insufficiency, Recurrent Candida infections).
“Without AIRE, your body will CHAR”.
20. Immunological tolerance. Central thymus-tolerance to self-antigens
The immune system has to fulfill two contradictory requirements: on the one hand the repertoire of different
antigen receptors needs to be as large as possible to avoid ‘holes in the repertoire’ that could be exploited by
pathogens to evade immune detection. On the other hand, the receptor repertoire must be shaped to prevent the
immune system from attacking the organism that harbors it. Any disturbance in this delicately balanced system can
have pathogenic or even lethal consequences, either from infections or from the unwanted reaction with
autoantigens or harmless external antigens as in allergy. Tolerance is the process that eliminates or neutralizes such
autoreactive cells, and a breakdown of this system can cause autoimmunity.
Immunological tolerance is the state of unresponsiveness to a particular antigen, mainly established in T and B
lymphocytes, breakdown of immunological tolerance to self antigens- cause of auto immune diseases.
T cell tolerance is established at two levels. Immature thymocytes undergo harsh selection processes in the
thymus. This is often called central tolerance and results in the deletion of most T cells with high affinity for self
antigens. Mature T cells are also regulated to avoid self-reactivity. The mechanisms that reinforce T cell tolerance
outside the thymus are collectively called peripheral tolerance.
Central tolerance refers to the selection processes which t cells precursors undergo in the thymus (proliferation,
differentiation and selection). Add positive and negative selection
21. Peripheral or post-thymus tolerance to self-antigens
Peripheral tolerance refers to the diverse mechanism that enforces and maintain T-cell tolerance outside the thymus,
includes prevention of contact between autoreactive T cells and their target antigens.
Includes1. Peripheral deletion- Autoreactive T cells are deleted by cytokine withdrawal or activation induced cell death
2. Anergy- Incapacity of T cells to carry out effector responses
3. Regulatory T cells (Tregs)- Responsible for suppressing immune system responses
22. Vaccination
Types of vaccination1) Live attenuated vaccine- Cellular and hormonal response.
Pros- Induces strong, lifelong immunity
Cons- May revert to virulent form
Eg- Adenovirus, Typhoid, Smallpox, BCG
2) Killed or inactivated vaccinationPathogen is inactivated by heat or chemicals. humoral response
Pros- Safer than live vaccines
Cones- Weaker immune response, booster shots are needed
Eg- Hepatitis A, typhoid, rabies (RAT)
23. Tumor immunology. Immune surveillance. Tumor- associated antigens
Ehrlich, who opined on all things immunological, believed that the immune system could protect the host from
cancer.
The immune surveillance hypothesis is often regarded as the intellectual underpinning of cancer immunology.
Although the hypothesis itself has contributed little to our attempts to treat cancer through immunological
means, it has profound implications for understanding the functions of the immune system.
Tumor-specific antigens defined by immunization all belong to the family of HSPs
When tumors were biochemically fractionated and individual protein fractions tested for their ability to elicit
protective tumor immunity, a number of tumor-protective antigens were identified in diverse tumor models, such as
mouse sarcomas, melanomas, colon and lung carcinomas, and rat hepatomas.
Interestingly, regardless of the tumor models used, all antigens were found to belong to the family of proteins
known as the heat-shock proteins (HSPs), which:
• could elicit protective immunity;
• were of the HSP90 (gp96 and HSP90), HSP70 (HSP110 and HSP/c70), calreticulin, and HSP170 (also known as
grp170) families.
HSPs must be isolated directly from tumors to be immunologically active. HSP molecules bind to APCs and target
peptides with high efficiency.
‘Tumor-specific antigens’ recognized by T cells show a wide spectrum of specificity
The tumor antigens identified as T cell epitopes fall into the following categories –
Cancer/testes antigens are expressed only in testes’
HSPs can chaperone many different types of antigen.
Differentiation antigens are lineage specific and not tumor specific
Unique tumor-specific antigens have been characterized in melanomas
T cell epitopes of viral antigens have been identified
24. Tumor immunology. Human tumor immune responses and escape mechanisms. Immunodiagnostics.
Immunotherapy
Immunotherapy1.
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Administration of BCG vaccine
Interleukins and interferons- immunomodulators
Tumor necrosis factor (effective against many solid tumors)
Monoclonal antibodies- against CTLA-4 and PD-1
Tumor Infiltrating Lymphocytes –Lymphocytes removed from cancer areas, grown, activated with IL-2 and
returned to the patient.
25. Primary immunodeficiency. B-cell deficiencies. Defect in phagocytes
There are two types of immunodeficiency disorders: those you are born with (primary), and those that are acquired
(secondary).
B-cell deficiencies
1- X-linked agammaglobulenemia (Bruton)- Affected males suffer from recurrent pyogenic infections. Defect in
BTK, Bruton tyrosine kinase gene, no B cell maturation.
2- Selective IgA deficiency- most common primary immunodeficiency.
Asymptomatic, atopy, anaphylaxisa
Low IgA levels
Can cause false-positive beta-HCG test.
3- Common variable immunodeficiency(CVID)- Defect in b-cell differentiation
May be present during childhood but diagnosis done in puberty.
low plasma cells,
low immunoglobulins. Recurrent infections of lower respiratory tract and gastrointestinal tract.
Phagocytotic defects
1-Chronic Granulomatous Disease - defective NADPH oxidase. Granules incapable of forming superoxide anion and
hydrogen peroxide which leads to the phagocyte not being destroyed.
2-Leukocyte adhesion Deficiency(LAD) – LAD1 CR3 receptor deficiency, leads to development of severe bacterial
infections, particularly of mouth and gastrointestinal tract.
In LAD2 a genetic defect of intercellular fucose transporter prevents fucosylation of membrane glycoproteins.
Consequently leukocytes cannot roll and cannot move into the extravascular place of inflammation.
LAD3 is due to impaired integrin signaling that also includes platelets. Patients suffer from severe infections and
increased bleeding.
26. Primary immunodeficiency. T-cell deficiencies. Defect in complement proteins
T cell deficiency
1- Severe Combined Immunodeficiency(SCID)- Affects various stages of T cell development or function.This
disease is due to mutation of common gamma chain shared by several cytokine receptors, namely those for
IL-2,4,7,9,15 and21. Interstitial pneumonia, protracted diarrhea and persistent candidiasis are common
clinical findings.
2- Th Cell deficiency- Failure to express MHC class 2 molecules on apc is inherited as an autosomal recessive
trait. Recurrent infections of respiratory and gastrointestinal tract.
3- DiGeorge anomaly – A congenital defect in the organs derived from third and fourth pharyngeal pouches. T
cell deficiency is variable. Majority have partial monosomy of 10p. Clinical manifestations include distinctive
facial features (low set ears, wide set eyes and shortened philtrum of upper lip), heart malformations or
aortic arch and neonatal tetany.
Complement defects
1-Hereditary Angioneurotic edema (HAE)- C1 inhibitor deficiency. Autosomal dominant trait. Recurrent episodes
of swelling of different parts of the body (angioedema).
2-Deficiency of classical pathway components leads C1q, C1r, C1s, C4 or C2 results in dev of complex diseases
such as Systemic Lupus Erythematosus.
27. Secondary immunodeficiency
Acquired immunodeficiency
Causes




Malnutrition
Viral infections (HIV)
severe burns
chemotherapy
radiation
Nutrient Deficiencies
Infection and malnutrition can exacerbate each other. Acts synergistically to depress immunity.
Poor nutrition can also cause deficits in innate immune defenses.
Zinc and Iron deficiencies can also affect immunity adversely. Zinc deprivation can cause severe progressive
involution of thymus, with rapid reduction in thymic weight (thus reduction and production and activity of
thymulin.)
Deficiencies in Vitamin C and E affects antioxidant functions, Vitamin A def impairs epithelial and mucosal
barriers and Vit D def leads toincreased infection rate.
Obesity increases susceptibility to serious risks of infections. There is alteration in levels of cytotoxicity,
NK cell activity and Ability of phagocytosis.
Drug induced Immunodeficiency
Several classes of drugs suppress immune function , either intentionally for therapeutic effect, or as an
unwanted side effect.
Iatrogenic immune suppression post-organ transplantation. Due to genetic differences causing the immune
system to perceive donor organs as foreign, recipients of organ transplants receive immunosuppressive regimens, often
longterm. Essentially the goal of these treatments is to prevent an immune response against either the host or donor
tissues while minimizing toxic side effects and susceptibility of the patient to infection. Drugs such as cyclosporin A and
tacrolimus.
Among the pharmacological agents that dampen immune responses, the glucocorticoids have the broadest
application. Glucocorticoids have pleiotropic effects that vary with both dose and duration of use; however, they are
perhaps best known for their potent anti-inflammatory effect. They have been the front-line drugs for decades in the
treatment of a variety of inflammatory and allergic conditions, and continue to be a major component of
immunosuppressive regimens following organ transplantation.
Human immunodeficieny virus causes AIDS
Infection with human immunodeficiency virus (HIV) is second only to malnutrition in causing immune deficiency and
is a significant cause of morbidity and mortality worldwide.
28. Hypersensitivity-Type I. Immunoglobulin E. Genetic of allergic response in Humans. Mast cells
Immediate (Type I) hypersensitivity responses are characterized by the production of IgE antibodies against
foreign proteins that are commonly present in the environment (e.g. pollens, animal danders, or house dust
mites) and can be identified by wheal and flare responses to skin tests which develop within 15 minutes.
The wheal and flare skin response is an extremely sensitive method of detecting specific IgE antibodies. The
timing and form of the skin response is indistinguishable from the local reaction to injected histamine.
Furthermore, the immediate skin response can be effectively blocked with antihistamines.
Most allergens are proteins Substances that can give rise to wheal and flare responses in the skin and to the
symptoms of allergic disease are derived from many different sources
IgE is distinct from the other dimeric immunoglobulins because it has:
• an extra constant region domain;
• a different structure to the hinge region; and
• binding sites for both high- and low-affinity IgE receptors, FceRI and FceRII
Production of IgE is dependent on T cells. It is also clear that T cells can suppress IgE production.
Cytokines regulate the production of IgE. Both IgE and IgG4 are dependent on IL-4.
Allergens have similar physical properties. The primary characterization of allergens relates to their route of
exposure. The routes includes:
• inhaled allergens;
• foods;
drugs;
• antigens from fungi growing on the body (e.g. Aspergillus spp.); and
• venoms.
The inhalant allergens cause hayfever, chronic rhinitis, and asthma
29. Hypersensitivity - Type I. Coetaneous reaction. Factors involved in the development of allergy. Hypo
sensitization
Mediators released by mast cells and basophils
The primary and most rapid consequence of allergen exposure in an allergic individual is cross-linking of IgE receptors on
mast cells and basophils:
• basophils are circulating polymorphonuclear leucocytes that are not present in normal tissue, but can be recruited to a
local site by cytokines released from either T cells or mast cells;
• mast cells cannot be identified in the circulation, but are present in connective tissue and at mucosal surfaces
throughout the body.
The process of degranulation in human mast cells and basophils involves fusing of the membrane of the granules
containing histamine with the plasma membrane. This process is initiated in most cases by cross-linking of two specific
IgE molecules by their relevant allergen.
An adverse cutaneous reaction caused by a drug is any undesirable change in the structure or function of the skin, its
appendages or mucous membranes and it encompass all adverse events related to drug eruption, regardless of the
etiology.
The primary method for diagnosing immediate hypersensitivity is skin testing. The characteristic response is a wheal
and flare.
• the wheal is caused by extravasation of serum from capillaries in the skin, which occurs as a direct effect of
histamine and is accompanied by pruritus (also a direct effect of histamine);
• the larger erythematous flare is mediated by an axon reflex.
Techniques for skin testing include:
• a prick test, in which a 25-gauge needle or a lancet is used to introduce 0.2 mL of extract into the dermis;
• an intradermal injection of 0.02–0.03 mL.
Immunotherapy (or hyposensitization) requires regular injections of allergen over a period of months. It is an
established treatment for:
• seasonal hayfever; and
• anaphylactic sensitivity to bees, wasps, and hornets.
In addition, immunotherapy is an effective treatment for selected cases of other allergic diseases including asthma.
The dose is increased progressively, starting with between 1–10 ng and increasing up to approximately 10 mg allergen
per dose. The response to treatment includes:
• an increase in serum IgG antibodies;
• a striking decrease in the response of peripheral blood T cells to antigen in vitro; and
• a marked decrease in late reactions in the skin. Over a longer period of time there is a progressive decrease in IgE
antibodies in the serum.
30. Hypersensitivity - Type II. Mechanisms of damage. Reactions against blood cells and platelets
Antibody-mediated (Type II) hypersensitivity reactions occur when IgG or IgM antibodies are produced against
surface antigens on cells of the body. These antibodies can trigger reactions either by activating complement
(e.g. autoimmune hemolytic anemia) or by facilitating the binding of natural killer cells.
In type II hypersensitivity, antibody directed against cell surface or tissue antigens interacts with the Fc
receptors (FcR) on a variety of effector cells and can activate complement to bring about damage to the target
cells. Once the antibody has attached itself to the surface of the cell or tissue, it can bind and activate
complement component C1. And cause activation of MAC.
Effector cells – in this case macrophages, neutrophils, eosinophils, and NK cells – bind to either:
• the complexed antibody via their Fc receptors; or
• the membrane-bound C3b, C3bi, and C3d, via their C3 receptors (CR1, CR3, CR4).
If the target is too large to be phagocytosed, the granule and lysosome contents are released in apposition to
the sensitized target in a process referred to as exocytosis.
However, when the target is host tissue that has been sensitized by antibody, the result is damaging.
Antibodies may also mediate hypersensitivity by NK cells. In this case, however, the nature of the target, and
whether it can inhibit the NK cells’ cytotoxic actions, are as important as the presence of the sensitizing
antibody.
Some of the most clearcut examples of type II reactions are seen in the responses to erythrocytes. Important examples
are:
• incompatible blood transfusions, where the recipient becomes sensitized to antigens on the surface of the donor’s
erythrocytes;
• hemolytic disease of the newborn, where a pregnant woman has become sensitized to the fetal erythrocytes;
• autoimmune hemolytic anemias, where the patient becomes sensitized to his or her own erythrocytes.
Reactions to platelets can cause thrombocytopenia, and reactions to neutrophils and lymphocytes have been
associated with systemic lupus erythematosus (SLE).
31. Hypersensitivity - Type II. Mechanisms of damage. Reactions against tissue antigens
A number of autoimmune conditions occur in which antibodies to tissue antigens cause immunopathological
damage by activation of type II hypersensitivity mechanisms. The antigens are mostly extracellular, and may be
expressed on structural proteins or on the surface of cells. The resulting diseases discussed here include
Goodpasture’s syndrome- antibodies to collagen type 4. Severe necrosis of glomerulus with fibrin deposition.
Pemphigus- Antibodies to intracellular adhesion molecules. Componenets of desmosomes gap junctions.
Myasthenia gravis.- Antibodies to acetyl choline receptors cause muscle weakness.
32. Hypersensitivity- Type III. Mechanisms in type III hypersensitivity. Experimental models of immune-complex
disease
Immune complexes are formed when antibody meets antigen, and generally they are removed effectively by the
liver and spleen via processes involving complement, mononuclear phagocytes and erythrocytes.
Immune complexes may persist and eventually deposit in a range of tissues and organs. The complement and
effector cell-mediated damage that follows is known as a type III hypersensitivity reaction or immune complex
disease.
Immune complex formation can result from:
• persistent infection;
• inhalation of antigenic material
• autoimmune disease;
• cryoglobulins.
Persistent infection with a weak antibody response can lead to immune complex disease. Immune complexes can be
formed with inhaled antigens. Immune complex disease occurs in autoimmune rheumatic disorders.
Immune complexes are capable of triggering a wide variety of inflammatory processes:
• they interact directly with basophils and platelets (via Fc receptors) to induce the release of vasoactive amines.
• macrophages are stimulated to release cytokines, particularly tumor necrosis factor-a (TNFa) and interleukin-1 (IL1), which have important roles in inflammation;
• they interact with the complement system to generate C3a and C5a, which stimulate the release of vasoactive
amines (including histamine and 5-hydroxytryptamine) and chemotactic factors from mast cells and basophils; C5a is
also chemotactic for basophils, eosinophils, and neutrophils.
Experimental models are available for the main types of immune complex disease described above:
• serum sickness, induced by injections of foreign antigen, mimics the effect of a persistent infection; • the
NZB/NZW mouse demonstrates autoimmunity;
• the Arthus reaction is an example of local damage by extrinsic antigen.
33. Hypersensitivity- Type III. Mechanisms in type III hypersensitivity. Persistence of complexes. Deposition of
complexes in Tissue. Detection of immune complex
Immune complexes may persist in the circulation for prolonged periods of time. However, simple persistence is
not usually harmful in itself; the problems start only when complexes are deposited in the tissues.
The most important trigger for immune complex deposition is probably an increase in vascular permeability.
Pretreatment with antihistamines blocks this effect.
Immune complex deposition is most likely where there is high blood pressure and turbulence.
The ideal place to look for immune complexes is in the affected organ. Tissue samples may be examined by
immunofluorescence for the presence of immunoglobulin and complement. The composition, pattern, and particular
area of tissue affected all provide useful information on the severity and prognosis of the disease.
34. Hypersensitivity- Type IV. Contact hypersensitivity. Cellular reaction in type IV hypersensitivity
Delayed-type hypersensitivity (DTH) is a T cell-mediated inflammatory response in which the stimulation of
antigenspecific effector T cells leads to macrophage activation and localized inflammation and edema within
tissues. This effector T cell response is essential for the control of intracellular and other pathogens. If the
response is excessive, however, it can damage host tissues.
The T cell response may be directed against exogenous agents, such as microbial antigens and sensitizing
chemicals, or against self-antigens. Typically T cells are sensitized to the foreign antigen during infection with the
pathogen or by absorption of a contact sensitizing agent across the skin.
Three variants of type IV hypersensitivity reaction are recognized (Fig. 26.1):
• contact hypersensitivity and tuberculin-type hypersensitivity both occur within 72 hours of re-exposure to
antigen;
• granulomatous hypersensitivity reactions develop over a period of 21–28 days – the granulomas are formed by
the aggregation of macrophages and lymphocytes and may persist for weeks – this is the most important type of
type IV hypersensitivity response for producing clinical consequences.
Contact Hypersensitivity
Contact hypersensitivity is characterized by an eczematous skin reaction at the site of contact with an allergen.
Sensitizing agents for humans include metal ions, such as nickel and chromium, many industrial chemicals including
those in rubber and leather and natural products present in dyes, drugs, fragrances and plants, such as
pentadecacatechol, the sensitizing chemical in poison ivy. Sensitizing agents behave as haptens.
A contact hypersensitivity reaction has two stages – sensitization and elicitation. Dendritic cells and
keratinocytes have key roles in the sensitization phase. Keratinocytes produce cytokines important to the contact
hypersensitivity response. Sensitization stimulates a population of memory T cells.
Elicitation involves recruitment of CD4þ and CD8þ lymphocytes and monocytes.
35. Hypersensitivity- Type IV. Tuberculin-type hypersensitivity. Granulomatous hypersensitivity
Tuberculin-type hypersensitivity
Tuberculin-type hypersensitivity was originally described by Koch. He observed that if patients with tuberculosis
were injected subcutaneously with a tuberculin culture filtrate (antigens derived from the causative agent,
Mycobacterium tuberculosis) they reacted with fever and generalized sickness. An area of hardening and swelling
developed at the site of injection.
This form of hypersensitivity may also be induced by T cell responses to non-microbial antigens, such as beryllium and
zirconium.
Granulomatous hypersensitivity
Granulomatous hypersensitivity is clinically the most important form of type IV hypersensitivity, as it is
responsible for the immunopathology in many diseases that involve T cell-mediated immunity. It usually results from the
persistence within macrophages of:
• intracellular microorganisms, which are able to resist macrophage killing; or
• other particles that the cell is unable to destroy.
Epithelioid cells and giant cells are typical of granulomatous hypersensitivity. A granuloma contains epithelioid
cells, macrophages, and lymphocytes.
36. Hypersensitivity- Type IV. Cellular reaction in type IV hypersensitivity. Diseases manifesting type IV
Granulomatous hypersensitivity
T cells bearing ab TCRs are essential.
IFNg is required for granuloma formation in humans.
TNF and lymphotoxin-a are essential for granuloma formation during mycobacterial infections.
There are many chronic human diseases that manifest type IV hypersensitivity. Most are due to infectious agents, such
as mycobacteria, protozoa, and fungi, although in other granulomatous diseases such as sarcoidosis and Crohn’s disease
no infectious agent has been established.
Leprosy is a chronic granulomatous disease of skin and nerves caused by infection with M. leprae. It is divided
clinically into three main types – tuberculoid, borderline, and lepromatous.
In tuberculosis, the granuloma provides the microenvironment in which lymphocytes stimulate macrophages to
kill the intracellular M. tuberculosis. The formation and maintenance of granulomas are essential to control the
infection.
In schistosomiasis, which is caused by parasitic trematode worms (schistosomes), the host becomes sensitized
to the eggs of the worms, leading to a typical granulomatous reaction in the parasitized tissue mediated essentially by
TH2 cells. In this case the cytokines IL-5 and IL-13 are responsible for the recruitment of eosinophils and the formation of
the granulomas around the ova.
Cause of sarcodiasis and crohns disease is unknown.
37. Transplantation and rejection. Barriers to transplantation. Histocompatibility antigens
Transplantation is the only form of treatment for all end stage organ failures.
There are many types of transplantations1.
2.
3.
4.
Isograft- From a genetically similar individual. Low chances of rejection.
Autograft- From one part to another. Eg: Trunk to arm.
Allograft- From one member of the species to another member of the same species.
Xenograft- From one species to another.
The differences that arise are known as allogenic differences.
Rejection
Graft Vs Host- When donor lymphocytes attack the recipients cells. Happens when competent immune cells are
transplanted into a recipient.
Host Vs Graft- The host body rejects the graft. In this case, immune system shows memory because of which a second
graft will be rejected more rapidly.
1.
There is a high frequency of T cells that recognize graft as foreign.
In infections, only 1/10000 T cells respond
In transplants, about 1/100 or 1/1000 cells respond.
2. Allospecific response
a) MHC class I- CD8 T-cells
b) MHC class II- CD4 T-cells.
38. Transplantation and rejection. The role of T lymphocytes in rejection. The tempo of rejection. Prevention of
rejection
Last option in organ failure. Bla bla isograft, allograft, autograft and xenograft.
Rejection1- Hyperacute Rejection
-Minutes to hours
-Pre-formed antidonor antibodies
Prevention- Avoiding transplantation into an individual who already has pre-existing antibodies.
Method to check- Incubating the donor leukocytes with recipient serum in presence of complement.
If there’s cell death- not compatible.
2- Acute Rejection
-Days to weeks
-Activation of alloreactive T-cells which are capable of damaging the graft.
Activated T-cells migrate to the organs and lead to tissue damage1. Generation of T-cells
2. Induction of delayed type of hypersensitivity.
3- Chronic Rejection
-Months to years
-Slow cellular response
Histological analysis- Thickening of intima
Prevention of Rejection1. By X-rays
2. Steroids
3. Cyclosporin- suppresses lymphocyte production
4. Azathioprine- blocks T cells proliferation
39. Autoimmunity and autoimmune disease. The association of autoimmunity with disease. Genetic factors.
Pathogenesis
An autoimmune disease is a condition in which your immune system mistakenly attacks your body. The immune
system normally guards against germs like bacteria and viruses. When it senses these foreign invaders, it sends out
an army of fighter cells to attack them.
ExamplesSystemic lupus erythematosus (SLE)- the joints, skin, brain, lungs, kidneys, and blood vessels.
Vasculitis- can range from a minor problem that just affects the skin, to a more serious illness that causes problems
with organs like the heart or kidneys.
Usually, several genes underlie susceptibility to autoimmunity.
Clearly, the vast majority of autoimmune diseases are not single gene disorders. Rather, they occur as a result of the
complex interplay of multiple genetic and environmental factors. Evidence from genome-wide association studies
has demonstrated that many genes contribute to disease susceptibility, i.e. autoimmunity is usually polygenic. Thus
the effect of variation in any one gene is by itself typically small.
Certain HLA haplotypes predispose to autoimmunity
Further evidence for the operation of genetic factors in autoimmune disease comes from their tendency to be
associated with particular HLA specificities (Fig. 20.6). For most autoimmune diseases, the MHC region which is
located on the short arm of chromosome 6, provides the strongest genetic component to disease susceptibility.
Genes outside the HLA region also confer susceptibility to autoimmunity
Although HLA risk factors tend to dominate, autoimmune disorders are genetically complex and genome-wide
searches for mapping the genetic intervals containing genes for predisposition to disease also reveal a plethora of
nonHLA genes (Fig. 20.7) affecting:
• loss of tolerance;
• lymphocyte activation (receptor signaling pathways and co-stimulation);
• microbial recognition;
• cytokines and cytokine receptors;
• end-organ targeting.
Autoimmune processes and pathology
Autoimmune processes are often pathogenic. When autoantibodies are found in association with a particular
disease there are three possible inferences:
• the autoimmunity is responsible for producing the lesions of the disease;
• there is a disease process that, through the production of tissue damage, leads to the development of
autoantibodies;
• there is a factor that produces both the lesions and the autoimmunity.
40. Autoimmunity and autoimmune disease. Etiology. Treatment
Autoimmune disorders can affect nearly every organ and system of the body.
1. Diabetes (Type I) – affects the pancreas. Symptoms include thirst, frequent urination, weight loss and an
increased susceptibility to infection.
2. Graves' disease – affects the thyroid gland. Symptoms include weight loss, elevated heart rate, anxiety and
diarrhoea.
3. Inflammatory bowel disease – includes ulcerative colitis and possibly, Crohn's disease. Symptoms include
diarrhoea and abdominal pain.
4. Multiple sclerosis – affects the nervous system. Depending on which part of the nervous system is affected,
symptoms can include numbness, paralysis and vision impairment.
5. Psoriasis – affects the skin. Features include the development of thick, reddened skin scales.
6. Rheumatoid arthritis – affects the joints. Symptoms include swollen and deformed joints. The eyes, lungs and
heart may also be targeted.
7. Scleroderma – affects the skin and other structures, causing the formation of scar tissue. Features include
thickening of the skin, skin ulcers and stiff joints.
8. Systemic lupus erythematosus – affects connective tissue and can strike any organ system of the body.
Symptoms include joint inflammation, fever, weight loss and a characteristic facial rash.
Treatment for autoimmune disorders








anti-inflammatory drugs – to reduce inflammation and pain
corticosteroids – to reduce inflammation. They are sometimes used to treat an acute flare of symptoms
pain-killing medication – such as paracetamol and codeine
immunosuppressant drugs – to inhibit the activity of the immune system
physical therapy – to encourage mobility
treatment for the deficiency – for example, insulin injections in the case of diabetes
surgery – for example, to treat bowel blockage in the case of Crohn's disease
high dose immunosuppression – the use of immune system suppressing drugs (in the doses needed to treat
cancer or to prevent the rejection of transplanted organs) have been tried recently, with promising results.
Particularly when intervention is early, the chance of a cure with some of these conditions seems possible.
41. Immunologique techniques. Antigen- Antibody interactions. Isolations of pure antibodies.
Immunologic techniques such as





immunofluorescence,
enzyme-linked immunosorbent assay,
antigen detection,
polymerase chain reaction, and
DNA hybridization
42. Immunological techniques. Isolation of lymphocyte population. Effector- cell assays. Gene targeting and
transgenic animals
Isolation of lymphocyte population
Density-gradient separation of lymphocytes on Ficoll Isopaque
Lymphocytes can be separated from whole blood using a density gradient. Whole blood is defibrinated by
shaking with glass beads and the resulting clot removed. The blood is then diluted in tissue culture medium and
layered on top of a tube half full of Ficoll. Ficoll has a density greater than that of lymphocytes, but less than that
of red cells and granulocytes (e.g. neutrophils). After centrifugation the red cells and polymorphonuclear
neutrophils (PMNs) pass down through the Ficoll to form a pellet at the bottom of the tube while lymphocytes
settle at the interface of the medium and Ficoll.
Isolating cell populations using their characteristic surface molecules
The presence of characteristic surface molecules expressed by cell populations allows the cell populations to be
isolated from each other using cell panning and immunomagnetic beads.
Isolation of lymphocyte sub populations – panning
Cell populations can be separated on antibody-sensitized plates. Antibody binds non-covalently to the plastic
plate (as for ELISPOT immunoassay) and the cell mixture is applied to the plate. Antigen-positive cells (Agþ) bind
to the antibody and the antigen-negative cells (Ag– ) can be carefully washed off. By changing the culture
conditions or by enzyme digestion of the cells on the plate, it is sometimes possible to recover the cells bound to
the plate. Often the cells that have bound to the plate are altered by their binding (e.g. binding to the plate
cross-links the antigen, which can cause cell activation). The method is therefore most satisfactory for removing
a subpopulation from the population, rather than isolating it.
Cell separation by immunomagnetic beads
Direct method
The beads are coated with a monoclonal antibody to the cellular antigen of interest, by either:
• direct binding to the bead; or
• binding the primary antibody to secondary antibody-coated beads.
The coated beads are then incubated with the cell suspension (or even whole blood) and the cells bound by the
antibody on the beads (positively selected cells) are immobilized by applying a magnetic field to the tube
(concentrating on the test-tube wall around the magnet). The non-immobilized cells (negatively selected) are
removed from the tube and the positively selected cells are recovered following washing and dissociation from
the antibody-coated beads. This method can be also used to remove an unwanted population of the cells from a
mixture. In this case the non-immobilized cells will be collected for further experiments.
Indirect method
The monoclonal antibody to the target cellular antigen is first added to the cell suspension. Following incubation
with the antibody, the cells are washed and mixed with beads coated with the appropriate secondary anti-Ig
antibody. Cells bound to the magnetic beads (positively selected) are then immobilized with a magnetic field and
the non-immobilized cells (negatively selected) removed. The positively selected cells are then washed and
dissociated from the beads. The microbeads available these days allow us to abandon the dissociation
procedure. They are so small that they can be left attached to the cell surface, and will not interfere with their
function.
Cell sorting
Cells can be isolated by their surface markers using a flow cytometer with a sorting function (cell sorter). The
sorter will direct the cells fluorescing due to a specific fluoresceinated antibody attached to them into a
collection vessel. Using the example discussed in Method box 2.1, cells with attached FITC-conjugated antibody
would be directed to one collection vessel for green cells and cells with attached PE-labeled (orange) antibody –
to separate collection vessel for orange cells.