Properties and functions of immunoglobulins
· 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 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
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 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 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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