IMMUNOGLOBULINS AND THEIR RELEVANCE TO THE IMMUNE SYSTEM

Immunoglobulins are antibodies. These antibodies are glycoproteins.The antibodies which make up the immunoglobulins are found in heavy chains represented by the symbols γ,α,µ,and so on.Examples of immunoglobulins include immunoglobulin G (IgG),immunoglobulin A (IgA),immunoglobulin D(IgD) and immunoglobulin E (IgE).These immunoglobulins play vital roles in the immune systems of human and they are usually associated with diseases and immune responses.



Immunoglobulin G(IgG) represented by the symbol γ is a monomeric protein with molecular weight of 146,000 and sedimentation co-effiecient 7s.It is the most abundant of the immunoglobulins contributing between 70-75% of total plasma immunoglobulins.It is able to cross the placenta and activate the complement system.It provides antibody activity in tissues,contributes to immunity against many infectious agent that are blood-borne e.g. bacteria,viruses,parasites and some fungi.
Immunoglobulin M(IgM) represented by the symbol µ and accounts for about 10% of the total serum immunoglobulin.It is a pentameric protein with a molecular weight of 970,000.IgM are highly efficient against particulate antigens such as bacteria,they bind complement with high degree of efficiency.It is of greatest importance in primary immune response to interact with a foreign antigen that is introduced into a host.IgM is associated with rheumatoid arthritis.




Immunoglobulin A(IgA) represented by the symbol α and consist of between 15-20% of the total serum immunoglobulins in humans.IgA is the predominant immunoglobulin in sero-mucous secretions such as saliva,tracheobronchial secretion,colostrums milk and urinogenital secretions.It has a molecular weight of 385,000(i.e the secretory IgA existing mainly in the dimeric form).The secretory IgA is protected from proteolysis by the secretory component.




Immunoglobulin D(IgD) constitute less than 1% of the total plasma immunoglobulin but it is known to be present in large quantities on the membranes of circulatory B-lymphocyte.It plays a role in antigen triggered lymphocytes differentiation.(I.e neutrophils, eosinophils, monocytes, and basophils).



Immunoglobulin E(IgE) is present in trace amount in serum.It is found on the surface membrane of basophils and mast cells in all humans.It may play a role in active immunity to helminthic parasites but it is more commonly associated with immediate hyper-sensitivity diseases such as asthma,hay fever and eosinophilia.