Murine B lymphocytes appear to be heterogeneous from a functional point of view. Thus, those B cells that give rise to antibody-producing cells can be divided into a subset that requires cooperation with T-derived lymphocytes and another subset that is T independent (1-6). Recently, it has been shown that the B-cell population also contains suppressor cells that regulate various functions of T cells (7)(8)(9)(10)(11) and that these suppressor cells seem to be different from antibody-producing cells (10, 11).There is contradictory evidence as to whether the response to different mitogens defines different B-cell subpopulations. In mice, Melchers and Andersson (12) concluded that PPD and lipepelysaccharide (LPS) I stimulate the same cell, whereas Gronowicz and Coutinho (13) The aim of this work was to test directly various alternative hypotheses that could explain the differences in the responsiveness of routine B lymphocytes with regard to various mitogens: (a) One cell possesses the receptors for various mitogens and can be stimulated by all known murine B-cell mitogens separately; (b) the ability to respond to various mitogens depends on the stage of maturation of the B cell; (c) there are different subsets of lymphocytes for different mitogens.We have chosen three well-known B-cell mitogens for this study; LPS (12), Nocardia water-soluble mitogen (NWSM) (18) and DxS (13). We have used the 5-bromo-deoxyuridine (BUdR) suicide technique of Zoschke and Bach (20). This should be a more critical method for ascertaining whether different cells respond to different mitogens by eliminating or inactivating those cells that respond to an initial mitogen.The specific killing by rabbit anti-mouse immunoglobulin serum and by antiIa alloantisera was used to investigate the presence of Ig and Ia on the surface of cells reactive to the above mitogens.1 Abbreviations used in this paper: BUdR, 5-bromo-deoxyuridine; CNRS, Centre National de la Recherche Scientifique; Con A, concanavalin A; DxS, dextran sulfate; LPS, lipopolysaccharide; NWSM, Nocardia water-soluble mitogen.
136J. ExP. MED.