Immunoglobulin having maxium molecular weight and is first to be synthesised in fetus?
Correct Answer: IgM
Description: Ans. C. IgM. (Ref. Ananthanarayan 7th/Pg.89).IgM: IgM constitutes 5-8 % of serum immunoglobulins, with a normal level of 0.5-2 mg per ml. IgM molecules are polymers of five four-peptide subunits, each bearing an extra CH domain# is a basic antibody that is produced by B cells. IgM is by far the physically largest antibody in the human circulatory system. It is the first antibody to appear in response to initial exposure to antigen. The spleen is the major site of specific IgM production# It is also the first immunoglobulin expressed in the fetus (around 20 weeks) and also phylogenetically the earliest antibody to develop.# IgM has a molecular mass of approximately 900 kPa (in its pentamer form)IgGMain antibody in 2deg (delayed) response to an antigen. Most abundant isotype in serum. Fixes complement, crosses the placenta (provides infants with passive immunity), opsonizes bacteria, neutralizes bacterial toxins and viruses.IgAPrevents attachment of bacteria and viruses to mucous membranes; does not fix complement. Monomer (in circulation) or dimer (when secreted). Crosses epithelial cells by transcytosis. Most produce antibody overall, but released into secretions (tears, saliva, mucus) and early breast milk (known as colostrum). Picks up secretory component from epithelial cells before secretion.IgMProduced in the 1deg (immediate) response to an antigen. Fixes complement but does not cross the placenta. Antigen receptor on the surface of B cells. Monomer on B cell or pentamer when secreted. Shape of pentamer allows it to efficiently trap free antigens out of tissue while humoral response evolves.IgDUnclear function. Found on the surface of many B cells and in serum.IgEBinds mast cells and basophils; cross-links when exposed to allergen, mediating immediate (type 1) hypersensitivity through release of inflammatory mediators such as histamine. Mediates immunity to worms by activating eosinophils. Lowest concentration in serum. IgMIgGIgA-IgDIgEHeavy chainmgadeAdult serum levels40-345-mg/dL650-1,500 mg/dL75-390 mg/dLTraceTraceFunctionsComplement activation, classic pathway++-- Opsonization-++--Antibody-dependent, cod-mediated cytotoxicity (ADCC)-+---Placental transport-+---Naive B-cell antigen receptor+--+-Memory B-cell antigen receptor (one only)-++-+Trigger mast cell granule release----+
Category:
Microbiology
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