IgM antibodies play an important role in primary defense mechanisms. They have been shown to be involved in early recognition of external invaders like bacteria and viruses, cellular waste and modified self, as well as in recognition and elimination of precancerous and cancerous lesions (By similarity). Immunoglobulin (Ig) molecules consist of two chains, one heavy chain (which can be alpha, delta, epsilon, gamma or mu) and one light chain (which can be kappa or lambda) each consisting of a variable and a constant region. An IgM molecule contains thus a mu heavy chain combined with either a kappa or a lambda light chains (By similarity). During differentiation, B-lymphocytes switch from expression of membrane-bound IgM to secretion of IgM. Mu' chain is expressed in bone marrow. Cleaved by a non-enzymatic process after Asn-96, yielding a glycosylated protein of 55 kDa. The process is induced by other proteins, and requires neutral or alkaline pH.