CHARACTERIZATION OF A HUMAN PLASMACYTOMA LINE

The TH line was established by bringing tumour cells from a multiple myeloma patient into suspension culture and subsequently cloning them by limiting dilution. The cultured cells show marked heterogeneity; there are ultrastructural differences between small and large TH cells, particularly with respect to the rough endoplasmatic reticulum (RER). Karyotyping revealed chromosome numbers in the triploid range, with many structural abnormalities, at the 14q32 region among others. A t(14;18) could not be demonstrated. TH was shown to have germline and a rearranged allele for kappa light chain, and only a single rearranged gene for heavy chain immunoglobulin. TH expressed PCA-1, CD9, CD28 and CD38 antigens, HLA class II, RER and kappa light chain, but few or no other antigens associated with the B-cell lineage. Light chain kappa and trace amounts of IgG3 were found intracellularly as well as in culture supernatant. The addition of IL-6 to cultures of TH increased proliferation, as well as the secretion of kappa light chain and the membrane expression of CD28 and CD38 antigens. Because TH has relatively few B cell markers on its membrane, it may be useful for the induction of monoclonal antibodies specific for human plasma cells. It also provides a model for the demonstration that IL-6 can act as a paracrine growth and differentiation factor for cells of myelomal origin.