IgM normally constitutes about 10% of serum immunoglobulins. IgM antibody is prominent in early immune responses to most antigens and predominates in certain antibody responses such as 'natural' blood group antibodies. IgM (with IgD) is the major immunoglobulin expressed on the surface of B cells. The gene for the mu constant region contains four domains separated by short intervening sequences.
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. It is found almost exclusively as an homopentamer in the serum. Membrane-bound IgM molecules are non-covalently associated with heterodimer of CD79A and CD79B.
Isoform 1: Secreted.
Isoform 2: Cell membrane; Single-pass type I membrane protein.
has not yet been referenced specifically in any publications.