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Properties and functions of immunoglobulins

Ig M is the main immunoglobulin produced early in primary immune response

Properties and functions of immunoglobulins

Ig M

·     Ig M is the main immunoglobulin produced early in primary immune response

 

·     It is present on the surface of all uncommitted B lymphocytes

 

·     IgM is a pentamer and the valence is 10

 

·     Ig M is the most efficient immunoglobulin in agglutination, comple-ment fixation and other antigen antibody reactions

 

·     It plays an important role in the defense against bacterial and viral diseases

 

·     It does not cross placenta

 

Ig G

·     Ig

 

·     G has two identical antigen binding sites and is bivalent

 

·     There are four subclasses namely Ig G1,Ig G2, IgG3 and IgG4

 

·     Ig G is the predominant antibody in secondary immune response

 

·     It plays an important role in defense against bacteria, viruses

 

·     It also neutralizes toxins

 

·     It crosses placenta and is found in large quantities in newborns

 

Ig A

1.     Ig A is found mainly in secretions like milk, tears, saliva and secre-tions of respiratory, intestinal and genital tracts

 

2.     It protects the mucus membranes against microbial attack

 

3.     As many microbes enter the body through these mucus membranes, Ig A offers the first line of defense

 

4.           Each IgA molecule consists of two H2L2 units and a J chain and a secretory component.

 

5.     The secretory component is a polypeptide synthesized by epithe-lial cells and it helps IgA to pass the mucosal surface

 

IgE

·     IgE antibody is present in increased quantities in allergic individu-als\

 

·     The Fc portions of the molecule binds to mast cells and eosinophils

 

·     When this antibody combines with its antigen on the mast cell sur-face, it leads to allergic response

 

IgD

·              IgD has no antibody function

 

·        It may act as antigen receptor on cells

 

·              In serum it is present in only trace amounts


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