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Changes in the phenotype and immunoglobulin secretion of human B cells following co-culture with cells of an EBV+ lymphoblastoid line or fusion with mouse plasmacytoma cells. Studies in short-term and long-term culture.

The mechanisms controlling immunoglobulin production have been studied in two types of immunoglobulin-secreting cell generated from human B cells. The first type (I) was produced by activation and transformation of B cells by co-culture with cells of an Epstein-Barr-virus-positive (EBV+) lymphoblastoid cell line (EBV-B-LCL). The second type (II) consisted of human/mouse hybrid cells produced by fusing human tonsil B cells with cells of a mouse plasmacytoma line. Both these methods, singly and in combination, have been widely used for initiation of cell lines secreting human monoclonal antibodies (MoAbs). The two cell types were of quite different phenotype with respect to human B cell antigens. In type I cells MHC Class II and the pan B antigens CD19 and CD37 were expressed at levels typical of cells at the B cell stage. The antigens CD23 and CD39 were expressed at the high levels characteristic of EBV-transformed B cells. Type II cells expressed few B cell antigens. MHC Class II, pan B and the CD23 and CD39 antigens were very weakly expressed and by 119 days post-fusion only CD38 was detectable on cells of the three lines studied; CD9 was on two and CD19 on only one of the three lines. Thus the phenotype of type I cells was influenced by EBV transformation but was otherwise typical of activated B cells. Whereas the human B antigen expression of the hybrid (type II) cells was at the low level encountered on human plasma cells. It is suggested that fusion of a human B cell to a mouse cell which is at the plasmacytoid stage of differentiation results in a switching off of the expression of human peripheral B antigens by a differentiation-linked mechanism. These results are considered in relation to the practical aspects of the production of human MoAbs and the theoretical aspects of control of the passage of B cells to a secretory stage of differentiation.