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Cells 
of
the immune system
Cells and Tissues of the immune
system
 The
cells of the adaptive immune
system are normally present:
a)Circulating cells in the blood and
lymph
b)Anatomically defined collection in
lymphoid organs
 Lymphocytes
 Antigen
presenting cells(APC)
 Effector cells
Clonal selection
Cells of the immune system
(lymphocytes)
 Lymphocytes
are the only specific
cells and are responsible for
specificity and memory
 They are 3 subsets ,different in
functions and protein products but
not in morphology
1-B cells
2- T cells(helper and cytotoxic)
3- Natural killer (NK) cells
B cell development
Pro B cell- Pre B cell-Immature B cellmature B cell- Activated B cell
proliferation
Plasma cell
differentiation
memory cell
B lymphocyte development
stem cell
 Pro B cells
CD19,CD10, µ heavy chain rearrangement
 Pre B cells
Pre antigen receptor expression
 immature B cells
IgM BCR expression,independent of antigen
and their encounter with it ,receptor
editing,cell death,functional
unresponsiveness
 Mature B cells

Mature B cells
Fetal liver stem cells …….B-1 B cell
 Bone marrow stem cells…..B-2 B cells….marginal
zone B cells and follicular B cells with Both IgM &
IgD
 B-1 B cells (CD5+)
found in peritoneum and mucosal sites
Limited diversity
Secrete IgM
 Marginal zone B cells
Located in the spleen
Express IgM and CD21
Respond to blood-borne microbes

B cell surface markers
B
cell receptor(Ag recognition)
 CD21or CR2 (B cell activation and EBV receptor)
 CD25 (binds IL- 2)
 CD40 (B cell activation)
 CD80 or B7(costimulator for T cell activation)
T cell subpopulations
T lymphocytes mature in the thymus
*Mature T cells :Th and Tc,TR
*T cells have CD4, CD8,TCR(αβ & )
,CD28,CD40L,CD2,CTLA-4(memory T cells have IL-7 R)
*T helper cells have 2 subsets :Th1 and Th2
are differentiate by cytokine pattern that
they produce.
*Th1=IFN-
*Th2 =IL-4 , IL-5,IL-10, IL-13
Effector cells
 Activated
Th cells
 Cytolytic T cells
 Plasma cells
 Mononuclear phagocytes
 Nk cells
NK cell activity
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