Which of the following immunoglobulin is a pentamer?: (A) IgG, (B) IgA, (C) IgM, (D) IgD
Answer is C. IgM Both secretory IgA (dimeric) and IgM (pentameric) have J chains IgM is the main immunoglobulin produced early in the primary immune response. IgM is present on the surface of viually all uncommitted B cells. It is a pentamer composed of five H,L, units (each similar to one IgG unit) and one molecule of J (joining) chain.