| Abstract: | To analyze functional mitogen recognition by reactive B lymphocytes, we studied the effects of bacterial lipopolysaccharide (LPS) on the growth of the WEHI 279.1 B lymphoma line (W279). We found that LPS inhibits, in a dose-dependent manner, the growth of W279 cells in culture and that it reduces the frequency of cells growing as clones under limiting dilution conditions. Furthermore, we show that differential reactivity of "wild-type" cells to increasing LPS concentrations reflects the heterogeneity in the lymphoma cell population and the frequencies of "resistant" variants to each mitogenic concentration. This allowed us to derive variant tumor cell lines and clones, no longer LPS sensitive, either from mass cultures or, in a single-step selection, under limiting dilution conditions in the presence of low and high concentrations of LPS. Although mitogen reactivity is progressively lost upon prolonged culture, resistance to LPS was found to be a stable trait in selected variants, suggesting that it results from loss of functional mitogen recognition by the reactive cells. The specificity of mitogen reactivity or resistance was shown by the fact that some of the variant clones are still reactive to T helper cell-derived factors and others are not. Thus reactivity to LPS and to T cell factors can be separated, suggesting that the cell lines described here provide new tools for the biochemical analysis of B cell activation. |
