Low molecular weight IgM. Detection using immunoblotting.

Two techniques for the definitive identification of low molecular weight (LMW) IgM have been compared, namely, filtration chromatography combined with nephelometry and a modified immunoblotting assay. The results indicate that the latter is a more sensitive and reliable technique. Furthermore the resolution of immunoblotting is such that it can distinguish additional oligomeric forms of IgM as well as monomeric IgM suggesting a disorder of polymerization of pentameric IgM. As the presence of LMW IgM in the sera of patients with various disorders is of prognostic significance the immunoblot technique merits consideration as a useful screening assay to detect this moiety.