Immune system

Lecture(7) IMMUNE SYSTEM
Dr.Baha, H. AL-Amiedi
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 1 960 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
1. genetic component
2. Haemopietic component
3. Reticulo endothelial component
4. complement component
5. Lymphoid component
6. mucosal component
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 .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 )
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
1. Thymus
2. Bursa
2-Secoundary lymphoid organs
1. Spleen
2. 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.
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 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
table .1 Comparison between B-lymphocytes and T-1ymphocytes
characteres B- lymphocytes T-lymphocytes
1- Origin
2-Differentiation
3- -Role

4- Mediator
(lymphokines)
5- Surface
Immunoglobulin
6-T- Surface marker
E — Rosette
7- Antigen
recognition Bone marrow
Bone marrow
Humeral immune response




-


+


-



-



- Bone marrow
Thymus
Cells mediated
Immune response

+

-

+

+CD


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-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
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 e f 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:

1. Neutrophil active phagocytic in m acute inflammation.
2. Eosinphils are phagocytic in condition like allergic inflammation, parasitic inflammation
3. Basophils cells will release of. pharmacologically active agents in anaphylactic and a topic allergy.
The Complement system
A plasma protein with 25 fraction these protein heat sensitive at 56 C for 30 minutes , the chemical structure of complement is polypeptide chains interconnected by disulfide bound.
The complement system plays a major role in host defense and the inflammatory process. The complement component synthesized in liver , spleen as well as enterocytes with 25 fractions. Nine fraction of which are involve in complement pathways which act as sequential manner and can be activated or inhibited , properdin is important on first exposure to Microorganism (first Immune Response)
Complement classical pathway in second exposure to microorganism (second immune response) complement defect associated with disease condition, Activators of complement system are of two types immunological &non-.immunology ,also complement system regulated
with inhibition factors.
Classical complement system pathway: The activation of this is
1) Antigen -Antibody.
2) Non - Immunological such as C-Reactive protein and staphylococus
Staphylococcus aureus protein A.

Alternative (properdine) Complement system pathway
1.The immunological activator lgG, IgA molecules
2. Non - Immunological Activator,
a. Lipopoly saccharide.
b. Copra, Venum factor.


The Mechanism of cell lyses with complement when fraction of complement system binding with the cell surface of cell. in present of’ antigen & Antibody it will non - equilibrium in permeability of cell wall non - equilibrium in protein synthesis process of hole in cells.
Non - equilibrium in metabolic of cells presence of hole in cell
wall and that will lead to lyses of cells
the function of complement system:
The complement play a wide range of biologial activites when activated:
1-Mediated Antigen-Antibody Reaction
2-Mediated inflammatory response
3-Facilitate phagocytosis.
4-Facilitate blood coagulation
5-Neutralize viruses effect & the effect of bacterial LPS
6-Play a role in the non-specific resistance to microbial infection
7-Associated with immune distraction - of blood cellular component
1.The immunological activator lgG, IgA molecules




Complement fixation test : This is very sensitive is very
sensitive test and is capable of detection Antigen & Antibody it is used
for serological diagnosis with principle : The ability of Antigen – Antibody
complex to fix complement used for diagnosis of disease
1. Spirochaetal disease e.g Sphilis (wasserman reaction)
2. Rickettsial disease e.g typhus fever.
3. Viral disease like lymphogranuloma venerum
4. Parasitic disease e.g kala-azar, hydatid cyst, amoebiasis