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“ Immunity is basically a biological term that describes a

state of having sufficient biological defenses to avoid infection, disease, or other

unwanted biological invasion ”

There are 2 types of Immunity

1) Innate Immunity/Inborn Immunity2) Acquired Immunity

The acquired Immunity is of two types.

1)Humoral/B-cell immunity: In this type of immunityThe body develops circulating Antibodies which are globulinMolecules in the blood plasma.

2)Cell Mediated/T-cells Immunity: Its achieved through

Formation of large number of activated T-lymphocytes.

Cell Mediated immunity is initiated by antigens,because

Acquired immunity does not develop until after invasion by a foreign organism or toxin,its clear that the body must have some mechanism for recognizing this invasion.

Each organism or toxin almost always contain one or more different specific chemical compounds in its makeup.

In general these are protiens or large polysaccharides

And it is they that initiate acquired immunity/cell mediated immunity.

Cell mediated immunity is the product of body”sLymphocytes which are located most extensivelyIn Lymph nodes,Spleen,Thymus,GIT and Bone marrow.

T-lymphocytes forms activated lymphocytesThat provide CMI.

After originating in the bone marrow the T-lymphocytes first migrate to the thymus gland.Here rapidly divide and develop extreme diversity for Reacting against different specific antigen.One thymic lymphocyte develop specific reactivity Against one antigen .then the next lymphocyte Develops specificity against another antigen . This Continues until thousand of different types of thymiclymphocytes with specific reactivity against manyThousand of different antigen which leaves the Thymus and spread through blood.

T-lymphocytes specificity

Millions of different types of preformed T-lymphocyteHave been stored in lymph tissues,each of these isCapable of forming only one type of T-cells withA single type of specificity and only the specific type Of antigen with which it can react can activate it.Once it is activated by its antigen it reproduce wildly.

Which are realesed into lymph and then carry to the blood and circulated.All the different lymphocytes that are capable ofForming one specific T-cell are called a Clone of lymphocytes.

Formation of memory cells

When a clone of T-lymphocytes are activated by an antigen,many of newly formed lymphocytes are preserved in the lymphoid tissues to become additional T-lymphocytes of that specific clone.these preseved cells or memory cells are derived from normal T-Cells that have learned how to overcome an invader by remembering the strategy used to defeat previous infection.

T-lymphocytes respond to antigens only when they Are bound to specific molecules called MHC protiensOn the surface of antigen presenting cells in the Lymphoid tissue.The antigens on the surface of Antigen presenting cells binds with receptor moleculesOn the surface of T-cells and destroyed.Three major types of antigen presenting cells are1)Macrophages2)B-lymphocytes3)Dendritic cells

Dendritic cells are most potent antigen presentingCells located through out the body.

The MHC protiens bind peptide fragmentsOf antigenic protiens that are degraded insideAntigen presenting cells and then transportThem to the cells surface.

Types of MHC protiens

1)MHC I protien which present antigens to cytotoxicT-cells2)MHC II potiens which presents antigens to T-HelperCells.The antigens on the surface of antigen presenting cellsBind with receptor molecules on the surface of t-cellsThere are as many as one lac receptors site on singleT-cell.

Types of T-cells

1)Helper T-cells

2)Cytotoxic T-cells

3)Suppressor T-cells

Mechanism of CMI

1)Entry of the foreign particles

2)Antigen presenting cells

3)Role of MHC in Antigen presenting cells

4)Action of T-cells

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