Existence of disulfide-bonded IgM-IgA, IgM-IgG and IgM-IgG fragment complexes in one patient

Immunoglobulin G paraprotein cross-reactivity with immunoglobulin M measurement

We report a case of IgG paraprotein cross-reactivity with IgM measurement in a patient with IgGkappa multiple myeloma and associated IgA and IgM immune paresis. IgM measurements using a Beckman-Coulter Synchron LX IgM reagent initially gave unmeasurably low IgM concentrations (<0.3 g/L) but IgM quantitation using later batches of reagent gave IgM concentrations of 13-42 g/L. Immunofixation confirmed the continued presence of the IgGkappa paraprotein band with suppression of IgA and IgM and analysis on the Behring BN2 and Beckman-Coulter Immage instruments showed IgM concentrations of <0.2 g/L. Immunofixation using the Synchron LX IgM reagent as antiserum confirmed binding of the Synchron LX IgM antiserum to the IgGkappa paraprotein. This case highlights the importance of checking all unexpected immunoglobulin measurements with previous results and immunofixation findings to avoid mistakes.

Bispecific IgA/IgM antibodies and their use in enzyme immunoassay

Two hybrid hybridomas secreting polymeric bispecific antibodies to human chorionic gonadotropin and calf intestinal alkaline phosphatase were produced by fusion of IgA- and IgM-secreting mouse hybridomas. Both hybrid antibodies were purified from ascitic fluid by size exclusion chromatography. An IgM-like fraction was shown to exhibit bispecific activity. Bispecificity was completely lost following mild reduction and alkylation. Both bispecific antibodies were used to develop a sensitive enzyme immunoassay for hCG.