Interleukin 1 can act as a B-cell growth and differentiation factor.

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Abstract
Splenic B lymphocytes specifically reactive to the hapten fluorescein (FLU) were prepared from nonimmune adult mice by affinity fractionation on hapten-gelatin. These FLU-specific B cells were cultured as single cells or in small numbers in 10-.mu.l wells either in the absence of any feeder, filler, or accessory cell or in the presence of 3T3 fibroblasts acting as filler cells. A selected batch of a "T-cell-independent" antigen FLU-Ficoll, which induces growth and differentiation only in the presence of lymphokines or cytokines acting as B-cell growth and differentiation factors (BGDF), was used as the antigenic stimulus. It was found that murine interleukin 1 prepared by recombinant DNA technology was an effective, although weak, BGDF when acting with antigen on B cells cultured either under filler cell-free conditions or in the presence of 3T3 cells. When the murine interleukin 1 was used in combination with recombinant human interlerukin 2, itself a weak but effective BGDF in the system, an additive effect was observed. The results challenge the notion that interleukin 1 is exclusively or even primarily an activating cytokine. This system, in which pure factors are able to act with specific antigen on single hapten-specific B cells, will prove helpful for the further dissection of the respective roles of the various factors that can act on B cells.