The physiology of B cells as studied with tumor models.

B-cell tumors have been extraordinary sources of information about antibodies, their genes, and the cells that express them. An important principle that has emerged from the study of lymphoid tumors is that the long-held view that malignant lymphoid cells are "frozen" at a fixed point in differentiation is not generally valid. Presentation of immunoregulatory signals to transformed B cells can profoundly influence their proliferation, morphology, differentiation, gene expression, and immunoglobulin synthesis. In addition to their responsiveness to immunoregulatory signals, some tumors of B lineage elaborate immunoregulatory signals. Until quite recently B-cell tumors were used primarily as monoclonal sources of molecules of immunological interest. While they continue to be important sources of receptors, growth and differentiation factors, differentiation antigens, and immunoregulatory factors, they are being used with increasing frequency to define the molecular events that occur in B cells subsequent to receipt of an immunoregulatory signal. While the use of tumor cells as models of normal cells is often viewed with some skepticism, it is difficult to find examples wherein tumors have been misleading. Quite to the contrary, B-cell tumors have regularly provided powerful tools for dissecting the molecular events that underlie B-cell development, function, and regulation.