Monoclonal IgM, IgA and IgG in the serum of a single individual: Immunofluorescence identification of cells producing the immunoglobulins

Abstract

Monoclonal IgM(ϰ) and IgA(ϰ) in the serum of patient CM were previously shown to share identical, individually specific (Ind) or idiotypic antigenic determinants. A component in the IgG fraction of CM's serum was shown by one of the assay systems to also share Ind determinants with the IgA and IgM. Recent experiments have indicated that the CM IgG monoclonal protein also shares identical Ind determinants with the other two CM immunoglobulins (Ig). These results suggested that the variable regions of the heavy and light chains of the three different classes of Ig were very similar. A direct immunofluorescence assay was used in this study on bone marrow smears of patient CM obtained at two different dates to identify the cells producing these Ig. The reaction of antisera specific for Ind determinants demonstrated that most plasma cells, whether containing IgM, IgA, or IgG, stained with the anti‐Ind antisera; this occurred irrespective of whether the anti‐Ind antisera were generated to the patient's IgM or IgA. The reaction with isotypic antisera revealed cell populations containing either IgM, IgA, or IgG and a significant cell population containing both IgM and IgA. The common occurrence of IgM and IgA‐containing cells which synthesize monoclonal Ig with shared Ind determinants provides evidence consistent with the IgM‐IgA pathway of differentiation of antibody‐producing cells. Further, the tendency toward decreasing numbers of IgM‐staining cells with concomitant increasing numbers of IgA and IgG‐containing cells suggests that the clones of cells producing these Ig were derived from a single precursor cell.