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CELLS& ORGANS OF IMMUNE MECHANISM. Origin & structure. IMMUNE CELLS. Fetal liver -------------yolk cells Blood cell precursors. Stem cells reside in bone marrow. Erythroid, myeloid& lymphoid series. Lymphocyte populations. T-Lymphocytes (cytotoxic &helper T-cells).

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Immune cells
IMMUNE CELLS.

Fetal liver -------------yolk cells

Blood cell precursors.

Stem cells reside in bone marrow.

Erythroid, myeloid& lymphoid series.


Lymphocyte populations
Lymphocyte populations.

  • T-Lymphocytes (cytotoxic &helper T-cells).

  • Precursors differentiate in the thymus.

  • B –Lymphocytes develop in the bone marrow,gut associated lymphoid tissue,spleen and lymph nodes.

  • The ratio of T to B cells is approximately 3:1.


T cells
T-Cells.

  • Constitute 65-80% of circulating small lymphocytes.

  • Life span is long(months-years).

  • Some (40%) develop in the gut associated lymphoid tissue(GALT)instead of thymus.

  • Precursors differentiate in the thymus mainly.


Thymic education
THYMIC EDUCATION.

  • CLONAL DELETION (by apoptosis)

  • Negative selection self tolerance.


Thymic education1
THYMIC EDUCATION.

  • Positive selection for T cells that react well with self reacting antigens.

  • T cells are produced that are selected to react with both foreign Ag and self MHC proteins.


Role of t cell receptors
Role of T-cell receptors.

  • During their passage through the thymus double +ve cells synthesize a highly specific antigen receptor (TCR).

  • The genes that encode the receptor are variable, diversity & joining genes that rearrange and are responsible for the ability of the T-cells to recognize millions of different antigens.


Formation of immunocompetent t cells
Formation of immunocompetent T cells.

  • T-cell precursors differentiate into immunocompetent T-cells within the thymus.

  • In the initial stage they differentiate into Double positive cells(both CD4&CD8proteins).

  • Later they express only one type of antigen receptor&contain either CD4 orCD8 type of receptor,depending on which type of cell they come into contact.


Differentiation of immunocompetent cells
Differentiation of immunocompetent cells.

  • The cells that come into contact with cells bearing class 1MHC protein,differentiate into CD8 +ve,while those that come into contact with class2MHC proteins differentiate into CD4+ cells.

  • The double positive cells are located in the cortex while the single positive cells are located in the medulla.


Mhc proteins
MHC PROTEINS

  • Class 1 MHC PROTEINS

  • These are glycoproteins found on the surface of virtually all nucleated cells.

  • The complete class 1 protein is highly polymorphic.

  • The polymorphism of these molecules is important in the recognition of self and nonself.



  • Class 11 MHC PROTEINS foreign grafts would be correspondingly improved.

  • These are glycoproteins found on the surface of certain cells, including macrophages, B cells, dendritic cells of the spleen, and Langerhans cells of the skin.

  • Like class 1 proteins, they have a hypervariable region that provides much of the polymorphism. They also have a constant region where the CD4 proteins of helper T cell binds.


Biologic importance of mhc
BIOLOGIC IMPORTANCE OF MHC foreign grafts would be correspondingly improved.

  • The ability of T cells to recognize antigen is dependent on association of the antigen with either class 1 or class 11 proteins.

  • Cytotoxic T cells respond to antigen in association with class 1 MHC proteins.

  • Helper T cells recognize class 11 proteins.

  • This requirement to recognize antigen in association with a “self” MHC protein is called MHC restriction



Antigen antibody reactions
Antigen-Antibody Reactions medical contexts.

  • Reactions of antigens with antibodies are highly specific.

  • Because of the great specificity, reactions between antigens and antibodies are suitable for identifying one by using the other.

  • This is the basis of serologic reactions.


  • The results of many immunologic tests are expressed as a medical contexts.titer, which is defined as the highest dilution of the specimen e.g. Serum that gives a positive reaction in the test serum.

  • A patients serum with an antibody titer of, for example, 1/64 contains more antibodies, i.e.

  • Is a higher titer than a serum with a titer for example 1/4.


Medical importance of serologic antibody based tests
Medical importance of serologic (antibody-based ) tests medical contexts.

  • Diagnosis of infectious diseases.

  • Diagnosis of autoimmune diseases.

  • Typing of tissue and blood before transplantation.


Types of diagnostic tests
Types Of Diagnostic Tests medical contexts.

  • Agglutination

    In this test the antigen is particulate (eg, bacteria and red blood cells)

    Antibody because it is divalent or multivalent , cross-links the antigenically multivalent particles and forms a lattice work, and clumping (agglutination) can be seen.

    eg. ABO blood group test is agglutination


  • Precipitation (Precipitin medical contexts.)

  • In this test the antigen is in solution.

  • The antibody cross-links antigen molecules in variable proportions, and aggregates (precipitates) form.

  • In this test the antigen is in solution. The antibody cross-links antigen molecules in variable proportions, and aggregates precipitates form


  • Radioimmunoassay (RIA) medical contexts.

  • This method is used for quantitation of antigens or haptens that can be radioactively labeled.

  • It is based on the competition for specific antibody between the labeled (known) and the unlabeled (unknown) concentration of material.


  • Enzyme-Linked Immunosorbent Assay (ELISA medical contexts.)

  • This method can be used for quantization of either antigens or antibodies in patient specimens. It is based on covalently linking an enzyme to a known antigen or antibody, reacting the enzyme linked material with the patients specimen, and then assaying for enzyme activity by adding the substrate of the enzyme.


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