Pentameric structure -
Ans. is 'a' i.e., Ig M o IgM is a pentameric immunoglobulin with five, four - peptide subunits.o The subunits are joined together by J chain.IgMo IgM is the earliest immunoglobulin class to be synthesized by the fetus. begining at 20 weeks of age.o As it is not transported across the placenta, the presence of IgM in the fetus or newborn indicates intrauterine infection and its detection is useful in the diagnosis of congenital infections such as syphilis, rubella and toxoplasmosis.o It normally circulates as pentamer.o It is the oldest immunoglobulin class.o It is the predominant antibody in primary antibody response.o It is short lived, disappearing earlier than IgGL. Hence, its demonstration in serum indicates recent infection.o Treatment with 2-mercaptoethanol selectively destroys IgM wdthout affecting IgG. This is a simple method for the differential estimation of IgG and IgM.o The isohemagglutinins (blood group anti A, anti B) are usually IgMo Being largely confined to the intravascular space, IgM is believed to be responsible for protection against blood invasion by microorganisms.o Monomeric IgM is the major antibody receptor on the surface of B lymphocytes for antigen recognition.o IgM is an important component of immune complexes in autoimmune diseases e.g. IgM antibodies against IgG in Rheumatoid arthritis.
IgM
IgG
IgA
IgD
Immunology