Selective Stimulation of IgM Synthesis in Mouse B Lymphocytes by Pokeweed Mitogen

Abstract

THE division of lymphocytes into thymus-derived (T) cells and bursa-equivalent-derived (B) cells is well established (reviewed in refs. 1–3). The result of antigenic stimulation in the B line of lymphocytes is a differentiation process, involving clonal expansion and ultrastructural changes, to give a specialized population of cells which synthesize and secrete immunoglobulin. In the study of these processes a major problem is the small number of cells involved in response to antigen, usually less than 1% of the total lymphocyte population. Clearly a system for activating large numbers of lymphocytes into immunoglobulin synthesis would offer considerable advantages. This seems to occur when mouse B lymphocytes are stimulated by pokeweed mitogen (PWM). In our experimental conditions, however, IgM is the only immunoglobulin class to be synthesized. The rational basis for our experiments rests on three previous observations: (1) PWM-stimulated lymphocytes develop rough endoplasmic reticulum^4,5 and might therefore be expected to be secreting cells; (2) a small proportion of enlarged (“blast”) lymphoid cells in PWM-treated human blood lymphocyte cultures contain immunoglobulin demonstrated by immunofluorescence⁶ and (3) the recent demonstration that mouse B lymphocytes are activated by PWM⁷.