Immune system
Lecture(8 ) 
Dr.Baha,Hamdi.AL-Amiedi
Ph.D.Microbiology
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Immune system :The Immune system 
comprise a network cells with each other
cooperates directly to reach the effectors
mechanism. and defense the body .against
invaders , back to the 1960 the immune
system has been structurally and functionally
confined to lymphoid organs .Recently
however immune system may be of six
component as in the following
Component of immune system
1-genetic component 
2-Haemopietic component
3-Reticulo endothelial 
component
4-complement component
5-Lymphoid component 
6-mucosal component 
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genetic component: The immune system 
structures &functions are encoded by set
of genes like control Immune response,
GVHR ,immunoglobulin synthesis and The
genes of MHC system involved in
rejection of foreign tissue from a region
known as the Major histocompatability
complex (MHC) that contain several
Polymorphic genes which expressed on
the surface of all nucleated cells consist
of two classes (class I and class II)
.These act as peptide receptors and are
important in Antigen presentation after
processing the Antigen .
T-Cell receptors complex
T-Cell asurface MHC I&MHC II
These epitopes peptides bind to MHC 
molecules and present on the cell surface
of antigen presenting cells like
macrophage, dendric cells
Class I + epitopes peptide(APC)= 
recognized by CD-8 T- Cell
(Intracellular infection ) 
Class II + epitopes peptide(APC)
=recognized by CD-4 T- Cell
(Extracelluler infection ) 

Processing and presentation of
antigens
Lymphoid component: The Lymphoid 
component consist of primary and secondary
Lymphoid organs. The primary Lymphoid
organs consist of Thymus, Bone marrow and
Bursa of fabricious while the secondary
Lymphoid organs consist of Spleen and
peripheral — Lymphoid nodes.
: Lymphoid System organs 
l- primary lymphoid organs 
Thymus 
Bursa 
2-Secoundary lymphoid organs 
Spleen 
lymph Nodes 
Lymphoid system
Thymus: It is so- called because 
shape it resemble the leaf of thymus
plant .each lobe can be seen divide
by septa of connective tissue into
series of lobular sub - compartments
the outer region of densely packed
and rapidly dividing lymphocyte
called cortex the central area of
more loosely arrange of lymphoid
and reticular cell called medulla
lymphocytes differentiation in
thymus are called T- lymphocyte
Thymus
Bursa: it is epithelial & lymphoid organ 
that is found only in bird it is very similar
to the thymus it is composed of numerous
lobes each which has cortical and
medullar area. The medullar and the
cortical regions are separated by layer of
epithelial cells. Bursa play role in birds in
differentiation of. B- lymphocytes.In
mammals the Bursa equivalent is not
known. It is suggested that bone marrow
may do this function.
The peripheral lymphoid s stem organ: 
The peripheral lymphoid system organ: 
Spleen : It is abright-red organ lying in the 
upper left quadrant of the a abdominal cavity it
is capsulated by coating of connective tissue
the spleen have two function.
1-It is the major site for removal and 
destruction of dead red blood cells.
2-It is important organ of immune system it 
has red pulp and white pulp ,there is
lymphocyte cuff around central arterioles in
spleen for production antibodies - also it
contain B- lymphocyte seeded sit in white pulp
of spleen while the red pulp of spleen is site for
seeded T- lymphocyte
Lymph node
2- Lymph Nodes: 
It is small lees than 1cm,it is bean-shape ,it is 
distributed through the entire body it is linked
to ether by lymphatic vessels .the principle
function of lymph nodes are captured the
foreign matter in the lymph circu1ation and as
a site for maturation of lymphocyte with in
lymphoid follicles in the cortical region of
lymph node the afferent lymphatic vessel is
the site of entering of foreign antigens to the
lymph node. The Lymphopoiesas happened in
bone marrow B-cells processed and matured in
bone marrow ,While T-cells initially developed
in Thymus in mammals Bursa equivalent as
site of B- cell development, bone marrow has
been suggested, There are several structural
difference between B-cell and T-cell and are
summarized in table.
Lymphocytes: 
They are small round cells found in 
peripheral blood ,lymph .lymphoid
organs and other tissue .They have
the function of the
*Storage of immunological memory 
*immune responses to specific 
antigens
*T-cells produce activation produce 
(lymphokines) and induce cells
mediated response .
T-Cell Receptor molecule (TCR) 
which are associated with the
Cluster of differentiation
marker(CD3) Which are
transmits signal to produce
lymphokines when (TCR) binds
an antigen that regulate the
function of other lymphocytes .
T-Cell divided into several
subsets with different function :
The T-cell Receptor
1-TH1 Helper cells or TH2 express 
CD4 molecules on their surface and
function by secreting cytokine( 1L4
, 1L5, 1L6 and IL 10) that promote
B-cell to produce antibody
2-CD8 + T cells function as 
cytotoxic (TC) cells and can kill
other cell , primarily these infected
by Virus.
Characters
1-Origin
2-Differentiation
3-Role
4-Mediater
5-Surface
Immunoglobulin
6-T-surface
marker(E-Rosett)
7-Antigen
recogonition
B-Lymphocytes
T-Lymphocytes
Bone marrow
Bone Marrow
Bon marrow
Thymus
Humeral immune Cells mediated
Response
Immune respons
+
+
-
_
+
+CD
T Cells 
Cytotoxic T Cells (TC) 
• Possess CD8 receptors on the 
surface. 
• activated into cytotoxic T 
lymphocytes (CTL). 
– CTLs recognize 
Ag + MHC I. 
– Kills target cell.(virus-infected or 
tumor cells) 
– Releases perforin or granzyme to 
kill. 
Figure 
B-cells divide and transform into plasma cells which
recognize
Antigen through synthesize Antibody molecule on
their surface
Lymphocyte Functions:
•B cells secrete their antigen receptors: antibodies.
Natural killer cells: 
Small percentage of lymphocytes 
3% of peripheral lymphocytes
lack features of B&T cells but
have significant immunological
roles.
* They are killing target cells 
without antibody and
independent M.H.C
* They are killing malignant cells 
and virus infected cells
Reticuloendothelial system: 
it s a System of cells and tissues whose 
function include principally phagocytosis and
degradation and antigen presentation on the
surface of the cells which including fixed
macrophage and Circulation in blood. It is filter
particular matter from blood. The cells of
Reticuloendothelial system organized into
dense sheet and fibers form sructura1 matrix
of spleen ,bone marrow and lymph nodes
The cells are mononuclear leukocytes in blood 
in liver is kuppfar cells in spleen is denderitic
cells in lung is alveolar cells… ect.
Haemopietic component: 
Macrophages and microphages: 
Macrophages of lymphoid system captured the 
particulate antigen such as bacteria it is large
of lymphoid cells in blood (monocytes) they are
produced by bone marrow .tissue macrophages
are denderic cells in spleen alveolar cells in
lung…. etc
Macrophages have function phagocytosis for 
the invading microbes.
Microphages are leukocytes of blood: 
Neutrophile :active phagocytic in acute 
inflammation.
Esinophile: are phagocytic in condition like 
allergic inflammation, parasitic inflammation
Basophiles :cells will release of. 
pharmacologically active agents in anaphylactic
and a topic allergy.
Neutrophile
Monocyte
Esinophile
Basophile
The
End
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