IGM HEXAMERS

There has been a universal tendency to regard IgM antibodies as pentam eric molecules comprising five immunoglobulin monomeric subunits joine d by a single J-chain protein. Is this the only form of secreted IgM, or are the possibilities more complex? In this article, Joseph Brewer and colleagues propose that the IgM polymers secreted in primary immun e responses may be more heterogeneous than previously believed and tha t, as a consequence, the biological activity of IgM may have considera ble flexibility.