Three monoclonal IgG components, an IgG4(Λ), an IgG2(κ) and an IgG1/IgG3 (κ) Gm(f,b) hybrid, in a single myeloma patient

Abstract

An unusual triclonal IgG combination in the serum of a 56‐year old male with clinical stage IIIB multiple myeloma is reported. The patient initially had an IgG4(Λ) monoclonal protein in his serum and later developed an IgG2(κ) and an IgG (κ) which possessed the characteristics of both IgG1 and IgG3 subclasses with an unusual combination of allotypic markers. Three M‐proteins did not share idiotypic determinants. A rare class‐switch recombination followed by mutation has been considered as a possible mechanism leading to this combination.

Immunoglobulin G paraprotein cross-reactivity with immunoglobulin M measurement

“…A shift in immunoglobulin production from IgG to IgM under treatment was a biologically plausible explanation for this finding, with cases of switching from IgG to IgD and IgGλ to IgGκ reported. 2,3 Other possibilities include the presence of IgG and IgM paraproteins with common variable regions in the heavy chains or the development of disufide-bonded IgG–IgM fragment complexes. 4,5 However, the failure to identify any IgM paraprotein in either the original or follow-up immunofixation, the identical electrophoretic mobility of the ‘IgM’ band identified with the Synchron reagent with the original IgGκ paraprotein band and the low IgM concentrations measured using the Immage and BN2 assays points to an methodological rather than biological cause for this phenomenon.…”