Late Appearance of an IgA(kappa) Monoclonal Protein in a Patient with IgG(kappa) Multiple Myeloma: Sharing of Idiotypic Specificities between the Two Serum Proteins

Abstract

A patient with an Ig[immunoglobulin]G(.kappa.) monoclonal serum protein developed in the course of the disease a 2nd monoclonal spike of the same L chain type and of the IgA class. The latter monoclonal protein progressively increased and eventually exceeded the 1st IgG(.kappa.) protein. Antigenic analysis of the 2 myeloma proteins demonstrated that they shared idiotypic determinants. Immunofluorescence studies, carried out with anti-.gamma. and anti-.alpha. reagents tagged with different fluorochromes, revealed that the 2 isotypes were produced by different plasma cells. The data are discussed in the prospect of a possible transitional mechanism from IgG to IgA synthesis within a single B [bone marrow derived] cell clone.