<prompt> Which of the following immunoglobulin is a pentamer?IgGIgAIgMIgD  <response>: 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. 