Primary in vitro plaque-forming cell response to DAGG-Ficoll: LPS-induced enhancement mediated by interleukin-1

The specific primary in vitro plaque-forming cell (PFC) response of C57B1/6 nu/nu spleen cells to the Type 2 T-independent (TI-2) antigen DAGG-Ficoll was analysed in the absence of T cell help in a serum-free medium. Lipopolysaccharide (LPS) enhancement of the antigen-specific response was shown to be mediated by soluble factors contained in the supernatants of LPS-induced bone marrow-derived macrophages. The activity of these supernatants was not associated with residual LPS, since the antigen-specific response of B cells from mice genetically deficient in LPS receptors was equally well enhanced. The activity of these supernatants was associated with interleukin-1 (IL-1) and partially purified IL-1 prepared from P388D1 cells also enhanced the primary in vitro response to DAGG-Ficoll. Limiting dilution analysis experiments showed that only in the presence of exogenously added IL-1 could a single cell type, presumably the B cells, be shown to be limiting.