Interleukin 1 induces proliferation in two distinct B cell subpopulations responsive to two different murine B cell growth factors.

Two distinct classes of B cell growth factor (BCGF) have been described. BCGF I induces proliferation of anti-IgM-activated B cells, whereas BCGF II acts on a subpopulation activated by dextran sulfate. We examined the effect on both these B cell subsets of a B cell growth and differentiation factor that copurifies with interleukin 1 (BGDF/IL 1) produced by the WEHI-3 cell line. Proliferation was induced by BGDF/IL 1 in cultures of normal spleen cells depleted of T cells and adherent cells and activated by anti-IgM or dextran sulfate. Little effect was observed in cultures of spleen cells from B cell-deficient CBA/N mice. In cultures of normal B cells activated with anti-IgM and dextran sulfate together, BGDF/IL 1 induced a proliferative response comparable with the sum of the responses to the factor and either stimulus alone. These results suggest that anti-IgM and dextran sulfate activate distinct and independent B cell subpopulations, both of which are responsive to BGDF/IL 1.