Properties and functions of immunoglobulins

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