Complex Formation between Monoclonal IgM and Albumin.

Immunoelectrophoresis of serum Sö showed an abnormal albumin line extended cathodically into the β‐region and a thick IgM line extended anodically into the α2‐region. These abnormalities were caused by noncovalent binding of albumin to a monoclonal IgM and continuous dissociation of the complex during electrophoresis. The complex formation was immunologically specific in that human, hut not bovine, albumin combined with IgM Sö. The combining sites on IgM ‐were localised to the Fabμ fragment. Albumin was probably univalent in the reaction, since monomerk human serum albumin combined but did not precipitate with IgM Sö, whereas soluble aggregates of human serum albumin precipitated with IgM Sö.