immunoglobulin-M (IgM)

Function

IgM antibodies play an important role in primary defense mechanisms
role in early recognition of external invaders like bacteria & viruses, cellular waste & modified self, as well as in recognition & elimination of precancerous & cancerous lesions.
the membrane-bound form is found in the majority of normal B cells alongside with IgD
membrane-bound IgM induces the phosphorylation of CD79A & CD79B by the Src family of protein tyrosine kinases
membrane-bound IgM is non-covalently associated with heterodimer of CD79A & CD79B
it may cause death of cells by apoptosis
it is also found in soluble form, representing ~30% of the total serum immunoglobulins where it is found almost exclusively as a homopentamer
after the antigen binds to the B cell receptor, the secreted form is secreted in large amounts
IgM strongly fixes complement (4+) by the classical pathway