Serum monoclonal IgM undetectable by cellulose acetate membrane electrophoresis in four patients with B cell...

A small amount of monoclonal IgM was demonstrated in the serum of four B cell malignant lymphoma patients in whom electrophoretically homogeneous protein bands were not detected by either cellulose acetate membrane electrophoresis or immunoelectrophoresis. By using anti-idiotypic (Id) antisera prepared against serum IgM, the M proteins were detected and identified as the products of malignant cells. These findings suggest that the use of more sensitive technics than the usual serum electrophoresis shows that the incidence of M proteins in B cell malignant lymphomas is higher than has been previously reported.