Evidence for shared idiotypy expressed by the IgM, IgG, and IgA serum proteins of a patient with a complex multiple paraprotein disorder.

The results of a comparative idiotypic analysis of multiple Ig paraproteins isolated from the serum of an individual patient, Ca, with Sjögren's syndrome and Waldenström's macroglobulinemia are reported. At initial presentation, Ca serum was found to contain two major paraproteins, an IgMkappa and an IgGkappa, together with a small elevation in the level of IgA protein. The patient's clinical course was characterized by dramatic and opposing changes in the respective serum levels of the IgMkappa and IgGkappa paraproteins over an extended time period that coincided in part with received chemotherapy. Idiotypic antigenic analysis of the IgMkappa and IgGkappa paraproteins revealed that the two monotypic proteins shared identical idiotypic determinants. The Ca IgA serum fraction, specifically isolated by an immunoabsorbent and free of any IgG and IgM, was shown to possess idiotypic determinants identical to the IgG and IgM proteins. In extensive tests of specificity, the idiotypic determinants shared by Ca IgM, IgG, and IgA proteins were not present in large excesses of heterologous IgM and IgG, nor on Ig molecules contained in a large number of normal and myeloma sera.