Lymphoid systemDr. Baha, Hamdi AI-Amiedi

Ph. D .Microbiology

:Lymphoid component

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

Lymphoid System organs:

l- primary lymphoid organs

.1-Thymus

2-Bursa

2-Secoundary lymphoid organs

1-Spleen

.2-lymph Nodes

Thymus:

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:

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 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.

a-It is the major site for removal and destruction of dead red blood cells.

-b-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

2- Lymph NodesIt is small lees than 1cm,it is bean-shape ,it is

distributed through the entire body it is linked to

other by lymphatic vessels .the principle function of

lymph nodes are captured the foreign matter in the

lymph circulation 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.

Tabel-compaer between B-&T-lymphocytes

Lymphocytes:

They are small round cells found in

peripheral blood ,lymph .lymphoid organs

and other tissue .They have the function

of the following:.

1-Recognition the antigen

.2-Storage of immunological memory.

.3-immune responses to specific

antigens

T-Cell Receptor molecul(TCR)

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 lymphokineswhen (TCR) binds an antigen that regulate the function of other lymphocytes T-Cell divide into several subset with different function.

1-TH1 Helper cells or TH2 express CD4 molecules on their surface and function by secreting cytokine( 1L4 , 1L5, 1L6 and IL10)

That promote B-cells divide and transform into plasma cells Which recognize Antigen through Synthesize &produce antibody on their surface humeral immune rseponses

2-CD8 + T cells function as cellaur immune response & cytotoxic (TC) cells can kill Tumor & other cell , primarily these infected by Virus.

.

Role of MHC Classes & CD4,CD8 in immune responses

Natural killer cells

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