Membrane immunoglobulin M (mIgM) (mIgM)

Membrane immunoglobulin M (mIgM), also known as the B cell antigen receptor (BCR), is the monomeric form of IgM expressed on the surface of naïve and immature B lymphocytes. It consists of two μ heavy chains (each with four constant domains: Cμ1-Cμ4, plus a transmembrane tailpiece) and two light chains (kappa or lambda), linked by disulfide bonds and non-covalent interactions. The μ heavy chain has an additional hydrophobic transmembrane domain (about 41 amino acids) for anchoring to the B cell membrane. As a BCR, mIgM recognizes antigens with high specificity via its variable domains, initiating B cell signaling, activation, proliferation, and differentiation into plasma cells or memory B cells. It plays a key role in primary immune responses, self/non-self discrimination, and B cell development. Unlike secreted pentameric IgM (sIgM), mIgM does not incorporate a J-chain and functions primarily in antigen detection rather than secretion or mucosal transport.

Other names

membrane-bound IgMmonomeric IgMB cell receptor (BCR)membrane IgMsurface IgM