IgM molecules with and without J chain in serum and after purification, studied by ultracentrifugation, electrophoresis, and electron microscopy.

IgM molecules in pure IgM preparations and in the corresponding sera from three patients with Waldenström's macroglobulinemia have been studied by analytical ultracentrifugation, rate zonal ultracentrifugation, agarose-polyacrylamide gel electrophoresis, and electron microscopy. One of the IgM preparations was without J chain, while the two others contained J chain. The experiments revealed that IgM with J chain consisted of pentameric molecules; whereas in IgM preparations without J chain the dominating molecules were hexamers, but also pentamers, tetramers, and even smaller molecules were found. In both types of IgM the molecules formed a wide range of aggregates, which were usually more abundant in the purified IgM than in serum. Some of the aggregates were kept together by noncovalent forces only.