Activation of BCL1 cells by polyclonal activators and inhibition of growth and IgM secretion by anti-IgM.

Abstract

Bacterial lipoprotein (LP) and lipopolysaccharide (LPS) both activated an in vitro line of the B-cell tumour BCL1 to IgM secretion, as determined by the protein A plaque assay. LPS but not LP activation was inhibited by polymyxin B. Activation with both LPS and LP resulted in a less than additive response. Several clones of BCL1 were tested, and all responded to both LPS and LP. Both LPS and LP induced broad dose-response curves in normal lymphocytes, recently cloned BCL1 cells, and cloned and synchronized (G1 phase) BCL1 cells. This suggests that the dose-response curve cannot be due to accumulation of responding cells with different threshold sensitivities for activation. We cannot exclude the possibility that the broad dose-response curve is due to a heterogeneity of the LPS or LP preparation. The results indicate that LPS and LP induce similar signals in BCL1 cells. Furthermore, binding to the cell membrane and activation of BCL1 cells by LPS or LP seem to be separate events. An anti-IgM antiserum inhibited spontaneous DNA synthesis and spontaneous and LP-induced IgM secretion of BCL1 cells. Equal inhibition was observed with F(ab')2 fragments but not with Fab fragments of the antiserum, suggesting that cross-linking of IgM bound to the cell surface membrane-induced inhibition. Supernatants from concanavalin A (Con A)-activated spleen cells induced BCL1 cells to secrete IgM. Fab anti-IgM added alone to BCL1 cells did not induce IgM secretion. Furthermore, Fab anti-IgM plus Con A supernatant did not induce a higher response than the supernatant alone. This suggests that inductive signals via the IgM receptor do not occur in BCL1 cells.