lymphoid system

Lymphoid component:
Dr.Baha.Hamdi.AL-Amiedi
Ph.D.Microbiology

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
-Secoundary lymphoid organs
. Spleen
. lymph Nodes
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- lymphocytes.
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:
1. Spleen : It is a .bright-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.
It is the major site for removal and destruction of dead red blood cells.
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 s1peen is site for seeded T- lymphocyte
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. There are several structural difference between B-cell and T-cell are summarized in table. I
Lymphocytes:
They are small round cells found in peripheral blood ,lymph .lymphoid organs and other tissue .They have the function of the following:.
Recognition the antigen
. 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 :
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.
B-cells divide and transform into plasma cells which recognize
Antigen through synthesize Antibody molecule on their surface .
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