Briefly Describe Immunoglobulin M.
1) It constitutes 5.8% of total immunoglobulins. It has a normal serum level of 0.5 to 2 mg/ml.2) it is a pentamer having a molecular weight of 900,000 Daltons and has a sedimentation coefficient of 19S. It is phylogenetically oldest immunoglobulin.3) It has a half-life of about 5 days.4) 5 monomers are arranged with their Fc fragments in the centre of the pentamer and the antigen binding sites towards the periphery of the molecule.5) It is the first immunoglobulin to be synthesized by the foetus beginning by about 20 weeks of age.6) It is 500-1000 times more effective than IgG in opsonization.7) It particularly gives protection against microorganisms and other larger antigens that have repeating antigenic determines on their surface.
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