Analysis of surface antigen expression of human immunoglobulin-secreting cells: phenotypic heterogeneity in normal counterparts of myeloma cells

Summary Human myeloma cells are malignant counterparts of plasma cells which represent the most differentiated B cells. Myeloma cells are, however, heterogeneous in their surface antigen expression (Katagiri et al, 1984, 1985), which may reflect that normal plasma cells have a spectrum of differentiation. To test this hypothesis, immunoglobulinsecreting cells (ISC) of non-neoplastic nature were studied with regard to their surface antigen expression by using a combination of reverse haemolytic plaque assay and complement-dependent cytolysis. Non-neoplastic ISC were found to have a broad spectrum of differentiation stages from the immature type of CD20+, HLA-DR+, CD38+ in the peripheral blood to the mature type of CD20–, HLA-DR–, CD38+ in the bone marrow. In patients with polyclonal B cell activation (PBA), ISC showed a more immature antigen expression in comparison with ISC in normal controls or patients without PBA. The surface antigen development of ISC was clearly demonstrated throughout the stages in the analysis of mitogen-induced ISC in vitro. No significant difference in the surface phenotype of ISC was found among heavy chain classes. Thus, non-neoplastic ISC show a spectrum of differentiation similar to that of myeloma cells, depending on the site where ISC are located, and on the degree of PBA in vivo.