The IMMUNE SYSTEM
AP Bio Chapter 43
Antibody Immune System Response - Medical Animation
http://www.youtube.com/watch?v=iVMIZy-Y3f8
Organs of the Immune System
Fig. 43-7
Interstitial fluid
Adenoid
Tonsil
Blood
capillary
Lymph
nodes
Spleen
Tissue
cells
Lymphatic
vessel
Peyer’s patches
(small intestine)
Appendix
Lymphatic system
Lymphatic
vessels
Lymph
node
Masses of
defensive cells
The Lymphatic System
• The lymphatic system aids the immune system
in removing and destroying waste, debris, dead
blood cells, pathogens, toxins, and cancer cells.
• The lymphatic system absorbs fats and fat-soluble
vitamins from the digestive system and delivers
these nutrients to the cells of the body where they
are used by the cells.
• The lymphatic system also removes excess fluid,
and waste products from the interstitial spaces
between the cells.
What about the spleen?
• It acts as a filter for blood as part of the
immune system. Old red blood cells are
recycled in the spleen, and platelets and
white blood cells are stored there.
The immune system recognizes foreign bodies
and responds with the production of immune
cells and proteins
Two major kinds of defense have
evolved:
• innate immunity and
• acquired immunity
• Innate immunity is present before any
exposure to pathogens and is effective
from the time of birth
• It involves nonspecific rapid
responses to pathogens
• Innate immunity consists of external
barriers plus internal cellular and
chemical defenses
• Acquired immunity, or adaptive
immunity, develops after exposure to
agents such as microbes, toxins, or
other foreign substances
• It involves a very specific response to
pathogens
Fig. 43-2
Pathogens
(microorganisms
and viruses)
INNATE IMMUNITY
• Recognition of traits
shared by broad ranges
of pathogens, using a
small set of receptors
• Rapid response
ACQUIRED IMMUNITY
• Recognition of traits
specific to particular
pathogens, using a vast
array of receptors
• Slower response
Barrier defenses:
Skin
Mucous membranes
Secretions
Internal defenses:
Phagocytic cells
Antimicrobial proteins
Inflammatory response
Natural killer cells
Humoral response:
Antibodies defend against
infection in body fluids.
Cell-mediated response:
Cytotoxic lymphocytes defend
against infection in body cells.
The IMMUNE SYSTEM
pathogens
skin
Innate response
Acquired response
Innate immunity of vertebrates
Physical
• Skin – low pH of skin secretions
• Mucous membranes lining digestive,
respiratory, genitourinary tracts trap
and remove microbes (with cilia in
resp)
Chemical
• Lysozyme – enzymes that attack microbial
walls, found in tears, saliva, and mucus
• Gastric juice – low pH
• Interferons – proteins produced by viralinfected cells to alert other cells to defend
against viral reproduction also stimulates
macrophages
• Complement – proteins in plasma that when
activated by microbial contact may lyse
cells, trigger inflammation, or assist
acquired defensive immunity
Complement aiding the acquired
immunity system
Cellular
• Macrophages – attack microbes in the
spleen and interstitial fluid (known as
monocytes in the blood)
• Neutrophils – most numerous phagocytizing
cells, phagocytize bacteria
• Eosinophils – attack multicellular parasites
• Dendritic cells – in contact with
environment, stimulate acquired immunity
system
• Natural killer cells (NK cells) – recognize
absence of self-markers on infected cells
macrophage
Neutrophils – first on the job
Eosinophils – attack multicellular
parasites
A dendritic cell
http://www.rockefeller.edu/interacti
ve/steinman/dendritic_cell_v5.swf
Dendritic cell
alerting the
acquired
immune
system
NK cell doing its job!
What are toll-like receptors?
• TLR’s are proteins that span
membranes in leukocytes and other
cells that recognize nonspecific
microbes that breach physical barriers
such as the skin or intestinal tract.
• They in turn activate the immune
system.
• Originally identified in insects.
TLR’s spanning the membrane.
Response
Toll-like receptors
Alert!
Microbes
entering!
http://www.youtube.com/watch?v=iVMIZy-Y3f8
Inflammatory response
• Redness, swelling, heat
• Damaged mast cells in connective tissue
release histamine which triggers dilation
and leakiness of blood vessels, activates
macrophages, promotes blood flow to the
area
• Fever – triggered by toxins or pyrogens
released by macrophages, stimulates
production of wbc’s, speeds tissue healing
• Septic shock – overwhelming systemic
inflammatory response
Fig. 43-8-3
Pathogen
Splinter
Chemical Macrophage
signals
Mast cell
Capillary
Red blood cells Phagocytic cell
Fluid
Phagocytosis
ACQUIRED IMMUNITY
(adaptive immunity)
• Job of lymphocytes that circulate in the
blood and lymph, conc in spleen and
lymph nodes
• Develop from pluripotent stem cells in
the bone marrow and liver of fetuses
• Become T cells after cells have
migrated to the Thymus or
• B cells that develop in the Bone
marrow
Where is the thymus gland?
How do the B and T cells work
with the innate immune system?
Signaling molecules (cytokines)
from macrophages and dendritic
cells activate them.
What are antigens?
• Antigens – proteins or polysaccharides
protruding from microbes or toxins
floating around (antibody-generating)
• Epitope (antigenic determinants) –
portion of the antigen recognized by
immune cells
Looks like
epitopes to
me!
Fig. 43-10
Antigenbinding
sites
Antigen-binding sites
Antibody A Antigen Antibody C
C
C
Antibody B
Epitopes
(antigenic
determinants)
How tricky are pathogens
• Antigenic variation – changing their
surface epitopes to be unrecognizable
• Some viruses go into a latency period
and “hide” from the immune cells
• AIDS does both of these.
There are millions of lymphocytes with
their own types of antigen receptors. How
is the great diversity of B and T cells
produced?
• They are determined during early
embryonic development by genetic
recombination
• Receptors have constant regions
and variable regions that are
specific for antigens.
Fig. 43-9a
Antigenbinding site
Antigenbinding
site
Disulfide
bridge
Variable
regions
C
C
Constant
regions
Light
chain
Transmembrane
region
Plasma
membrane
Heavy chains
B cell
(a) B cell receptor
Cytoplasm of B cell
Fig. 43-9b
Antigenbinding
site
Variable
regions
V
V
Constant
regions
C
C
Transmembrane
region
Plasma
membrane
 chain
 chain
Disulfide bridge
Cytoplasm of T cell
(b) T cell receptor
T cell
What prevents B and T cells from
reacting against the body’s own
molecules?
• Lymphocytes with receptors specific for
body’s own molecules are either
inactivated or destroyed by apoptosis.
This is called self-tolerance.
How to distinguish self from nonself
• MHC molecules are so named because
they are encoded by a family of genes
called the Major Histocompatibility
Complex They identify cells as
belonging to you!
(histo = tissue)
• Class I MHC molecules are found on
almost all nucleated cells of the body
• Class II MHC molecules are found on
immune cells such as dendritic cells,
macrophages, and B cells.
They digest antigens and display pieces
of the antigen with their MHC complex
and are called antigen-presenting cells
(APC’s).
Class I – body cells
Class II- immune cells
Once the cells engulf the antigens, they
display them on their MHC complexes:
“SELF-NONSELF”.
• Cytotoxic-T cells will bind to the MHC I
complexes (recognize infected cells)
• Helper T- cells will bind to the MHC II
complexes. MHC II cells are called
APC’s (Antigen Presenting Cells).
Fig. 43-12
Infected cell
Microbe
Antigenpresenting
cell
1 Antigen
associates
with MHC
molecule
Antigen
fragment
Antigen
fragment
1
Class I MHC
molecule
1
T cell
receptor
(a)
2
2
Cytotoxic T cell
Class II MHC
molecule
T cell
receptor
2 T cell
recognizes
combination
(b)
Helper T cell
Immunological Memory
• When antigens react with the immune
cells, the cells that are specific for
that antigen are activated to divide
repeatedly and differentiate into clones:
• Effector cells – combative cells
• Memory cells – which carry receptors
for that particular antigen
• This is called CLONAL SELECTION.
Fig. 43-14
Antigen molecules
B cells that
differ in
antigen
specificity
Antigen
receptor
This one!
Clonal
selection
Antibody
molecules
Clone of memory cells
Clone of plasma cells
Monoclonal Antibody Production
Monoclonal Antibody Production
• The first exposure to a specific antigen
represents the primary immune
response
• During this time, effector B cells called
plasma cells are generated, and T cells
are activated to their effector forms
• In the secondary immune response,
memory cells facilitate a faster, more
efficient response
Fig. 43-15
Antibody concentration
(arbitrary units)
Primary immune response
to antigen A produces
antibodies to A.
Secondary immune response to
antigen A produces antibodies to A;
primary immune response to antigen
B produces antibodies to B.
104
103
Antibodies
to A
102
Antibodies
to B
101
100
0
7
Exposure
to antigen A
14
21
28
35
42
Exposure to
antigens A and B
Time (days)
49
56
Remembering the antigen!
Vaccines stimulate a mild
primary response so body can
wage a secondary response to
recognize another attack.
Acquired Immunity: 2 types:
Humoral and Cell-mediated
Humoral Immune Response
(antibody-mediated response)
• involves B cells and
• production of antiBodies in response to
free-floating antigens or those on
surface of foreign cells
B cells mature into plasma cells that produce
antibodies.
Cell-mediated Response
• involves cytotoxic T cells that destroy
target infected cells
The central role of Helper-T’s
• Immune cells (class II MHC) engulf
antigens and display them on their
MHC.
• Specific helper-T’s recognize the MHCantigen complex.
Binding to the helper-T
Displaying the antigen
• A T-cell surface protein called CD4 binds the
helper-T to the MHC-II.
• Activated helper-T’s release cytokines
(interleukins)
- result in more specific help-T’s and
memory cells being produced.
- stimulate both cell-mediated and
humoral responses
Fig. 43-17
The central role of Helper-T’s
Antigenpresenting
cell
Peptide antigen
Binds
Bacterium
Class II MHC molecule
CD4
TCR (T cell receptor)
Helper T cell
Humoral
immunity
(secretion of
antibodies by
plasma cells)
Cytokines
+
+
B cell
Animation: The Immune Response
+
+
Cytotoxic T cell
Cell-mediated
immunity
(attack on
infected cells)
Cell-mediated Response, how?
• When a nucleated regular cell becomes
infected, pieces of antigens are
combined with the MHC I and they
bond to cytotoxic T cells with the help
of CD8 surface proteins.
• The cytotoxic cell becomes a killer cell
which releases perforin that punches
holes in the infected cell.
• CD 8’s and CD 4’s are like bungy
cords.
They hold
the MHC
to the T or
B cells
Cell Mediated Immunity
Response of Cytotoxic T cells
Cytotoxic T-cell Activity Against Target Cells
Fig. 43-18-3
Released cytotoxic T cell
Cytotoxic T cell
Perforin
Granzymes
CD8
TCR
Class I MHC
molecule
Target
cell
Dying target cell
Pore
Peptide
antigen
Humoral Response, how?
• The B cell takes in a few foreign
molecules and presents antigen
fragments in its class II MHC to
activated helper-T cells.
• The activated B cell then proliferates
into a clone of plasma cells that will
produce antibodies and a clone of
memory B cells. (Some do not require
T-cell binding or cytokines.)
Fig. 43-19
Antigen-presenting cell
Bacterium
Peptide
antigen
B cell
Class II MHC
molecule
TCR
Clone of plasma cells
+
CD4
Cytokines
Secreted
antibody
molecules
Endoplasmic
reticulum of
plasma cell
Helper T cell
Activated
helper T cell
Clone of memory
B cells
2 µm
Humoral Immunity
T-Cell Dependent Antigens
Interaction of Antigen Presenting Cells and T-helper Cells
The cartoon illustrates how an antibacterial
antigen-specific immune response is generated.
Microbes invade the body and are captured by dendritic cells
(DCs, the ‘policemen’). The DC presents the antigen to the B
and Th cells.
The B cells respond by
“bombing” the microbes with
antibodies.
Putting it all together…
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter24/animatio
n__the_immune_response.html
Fig. 43-16
Humoral (antibody-mediated) immune response
Cell-mediated immune response
Key
Antigen (1st exposure)
+
Engulfed by
Gives rise to
Antigenpresenting cell
+
Stimulates
+
+
B cell
Helper T cell
+
Cytotoxic T cell
+
Memory
Helper T cells
+
+
+
Antigen (2nd exposure)
Plasma cells
Memory B cells
+
Memory
Cytotoxic T cells
Active
Cytotoxic T cells
Secreted
antibodies
Defend against extracellular pathogens by binding to antigens,
thereby neutralizing pathogens or making them better targets
for phagocytes and complement proteins.
Defend against intracellular pathogens
and cancer by binding to and lysing the
infected cells or cancer cells.
Hematopoetic stem cells in
bone marrow differentiate
Cells present in
Types of Antibodies
• Antibodies are proteins
that are made of light
and heavy chains.
• There are 5 different
antibodies: IgM, IgG,
IgA, IgD, and IgE. IgG
is the most abundant.
• IgE – antibodies
involved in allergies
Respond to
Different
antigens
IgE Mediated Hypersensitivity
• Initial exposure, helper T cells bind to
exposed antigens on immune cells.
• Cytokines stimulate the production of B
cells specific for IgE antibodies.
• Second exposure, those antibodies
bound to mast cells bind to the allergic
antigens which cause the mast cells to
release histamines and start an allergic
response. IgE Mediated Hypersensitivity
Antibodies label antigens for disposal by
1) Neutralization – blocking the ability of
a virus or bacterium to infect a host
cell by binding to its surface
2) Opsonization – antibodies (opsonins)
coat microbes for phagocytosis by
macrophages
opsonization
3) Antigen-antibody
complexes on microbes
can activate the
complement system and
trigger a membrane attack
complex (MAC).
Y’s and C’s
having a
party!
Fig. 43-21
Viral neutralization
Opsonization
Activation of complement system and pore formation
Bacterium
Complement proteins
Virus
Formation of
membrane
attack complex
Flow of water
and ions
Macrophage
Pore
Foreign
cell
Active and Passive immunity:
• Active – production of antibodies
from exposure or from
immunization
• Passive – temporary immunity by
antibodies supplied from the
placenta, mother’s milk, or
antibody injection
Immune Rejection
• Blood Matching: Antibodies to
blood group antigens can
stimulate an immune response.
• A person will make antibodies to
other blood antigens than its own.
You make antibodies against any
blood antigens you do not have.
• Transplanted tissue and organs are rejected
due to foreign MHC molecules. The use of
closely related donors and immune
suppression drugs help to minimize
rejection.
• In bone marrow transplants, the recipient’s
bone marrow cells are destroyed by
radiation, eliminating the recipient’s immune
system.
• The lymphocytes in the bone marrow
transplant may produce a graft versus host
reaction to the host cells if the MHC
molecules are not
closely matched.
Immune System Disorders
• Allergies are hypersensitivities to
certain environmental antigens, or
allergens.
- IgE antibodies produced in an initial
exposure may bind to mast cells and
cause a histamine response.
• Anaphylactic shock is a severe
allergic response in which
vasodilation leads to a lifethreatening drop in blood pressure
Autoimmune disease – immune
system turns against itself
• Ex - lupus, rheumatoid arthritis,
insulin-dependent diabetes mellitus,
and multiple sclerosis.
rheumatoid arthritis
Lupus
Systemic lupus
erythematosus (SLE) is a
long-term autoimmune
disorder that may affect
the skin, joints, kidneys,
brain, and other organs.
Multiple Sclerosis
• Multiple sclerosis (or MS) is a chronic,
often disabling disease that attacks the
central nervous system (CNS).
• Symptoms may be mild, such as
numbness in the limbs, or severe, such
as paralysis or loss of vision.
• The body’s own defense
system attacks myelin,
the fatty substance that
surrounds and protects
the nerve fibers in the
central nervous system.
The nerve fibers
themselves can also be
damaged.
• Immunodeficiency – may be developmental
(genetic) or in response to a chemical,
drugs, cancer, viruses (HIV).
• Severe combined immunodeficiency (SCID),
is a genetic disorder in which both B cells
and T cells) of the adaptive immune system
are impaired due to a defect in one of
several possible genes.
• Exercising to exhaustion and stress can
impair the immune system.
Enzyme-Linked
ImmunoSorbent Assay
(ELISA)
used to detect antibodies
Generalized ELISA protocol for
detecting a target antigen. Enzyme (E)
is conjugated to secondary antibody.
Bind
sample(antigen) to
support
Add primary antibody;
wash
Add secondary antibody-enzyme
conjugate; wash
Add substrate. If enzyme is present,
then a color change (blue) will occur.
The need for controls
• Positive – primary antibodies
- to make sure assay is working
• Negative – buffer
- to make sure all samples are not
positive and thus get a false positive
HINTS!
• Label correctly!
• Do not contaminate!
• You can use 40 uL instead of 50 uL with
the micropipettes. Amounts are not
critical. This is a qualitative test!
• If you mess up, you will have to repeat
the test AFTER SCHOOL!
If serial dilutions are used, you can
see different intensities of
antibodies present.
Cell signaling and immunology
• In cells of the immune system,
signaling leads to activation of cell-type
specific immune activities.
• Ligand interaction with receptors on
the surface of cells of the immune
system triggers intracellular signal
transduction directly or through
association with assistant signal
transduction molecules.
Immune signaling serves a
variety of functions:
• apoptotic deletion of cells bearing
receptors against self-peptides
• activation of immune and inflammatory
response activities
Signaling in the innate response
• Toll-like receptors (TLRs) appear to be
one of the most ancient, conserved
components of the immune system,
and are the basic signaling receptors of
the innate immune system.
• TLRs trigger signals evoking synthesis
and secretion of cytokines and
activation of host defenses through
various pathways.
Cytokines – cell to cell
• secreted by immune cells in response to
cellular signaling, and bind to specific
membrane receptors, which then signal the
cell via second messengers, often tyrosine
kinases, to alter cellular activity (gene
expression).
• Interleukins comprise the largest class of
cytokines, and are manufactured by one
leukocyte to act on other leukocytes as
signaling ligands. Cytokines are often
produced in cascades.
Cytokine Signaling
Signaling in the adaptive
immune response :
Ligands:
• Antigens
• MHC processed peptide pieces
• Hematopoietic growth factors (cause
blood cells to grow and mature)
Signal Transduction:
• Tyrosine-kinases
• 2nd messengers: Ca+ ions, IP3,
G-proteins, etc.
• Activation of transcription factors
Response:
• Transcribe mRNA into proteins for
immune activation