Transcript Tissues of the immune system

Types of lymphoid tissues
A- Generative organs or primary lymphoid
organs
The sites for cell proliferation and maturation
Such as Bone marrow and thymus
B- peripheral lymphoid organs or secondary
organs
Where lymphocytes responses to foreign Ags
Such as :spleen ,lymph nodes,cutaneous and
mucosal immune system .
Bone marrow
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Stem cells in bone marrow express CD34 and
stem cell antigen -1(sca-1)
Proliferation and maturation of precursor cells
are stimulated by cytokines(CSFs)produced by
stromal cells and macrophages
Plasma cells,stem cells and their progeny
Thymus
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The site of T cell maturation
Bilobed organ divided into multiple lobules
and each lobule consists of an cortex and an
medula
Thymus contain thymocytes and non lymphoid
cells
Why peripheral lymphoid tissues?
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1)To optimise the cellular interaction ,
lymphocyts and APCs are localised and
concentrated in anatomically defined
tissues.(immune response)
2)The sites where foreign Ags are transported
and concentrated. (Ag trapping)
Peripheral lymphoid tissues
(lymph nodes)
The skin ,epithelia and
parenchymal organs contain
many lymphatic vessels that
absorb and drain interstitial
fluis from this sites.
The absorbed interstitial fluid
, called lymph.
(lymph node)
* The Cortex consist of follicles
* Follicles are the B cell zones of
lymph nodes
* The T cells are located beneath
and between the follicles
* The naïve T cells express CCR7
and its ligand is CCL19 ,CCL21
* The naïve B cells express CXCR5
and its ligand is CXCL13
(lymph node)
(spleen)
* Major site of immune responses to
blood borne antigens.
* White pulp:
a) Periarteriolar lymphoid
sheaths(PALS) is the T cell zone of
spleen
b) Lymphoid follicles
c) The Marginal zone is a rim of
lymphocytes and macrophages that
surround the follicles
*individuals lacking a spleen are
extremely susceptible to infections
with encapsulated bacteria
White pulp
(MALT)
(mucosal associated lymphoid tissues)
Mucosal associated lymphoid tissues(MALT)
* In the mucosa of the gastrointestinal tract
lymphocytes are found in :
a)Within the epithelial layer :T cells and 10% 
b)Scattered throughout the lamina propria:T cells ,B
cells ,MØ,plasma cells,DC ,EO,Mast cells
c)In Peyers patches
• M cells
Immunity to oral Ags differ in some respects
a)High levels of IgA production
b)Tendency of oral immunization with protein
antigens to induce T cell tolerance
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