high molecular weight immunoglobulin, consisting in humans of five basic units (of two light and two heavy chains) arranged as a pentamer and joined together by disulphide bonds and a small link peptide (J chain) ... IgM activates complement very effectively but does not cross the human placenta. IgM antibodies are the first to be synthesized and released after a primary antigenic simulation, and are the predominant form made in response to many bacterial capsular polysaccharides ..., makromolekulaarne, mh. punalibledega ja bakteritega reageeriv immunoglobuliin, mis osaleb esmases immuunvastuses