Lipopolysaccharide-induced activation of suppressor cells: reversal by an agent which alters cyclic nucleotide metabolism.

The effects of bacterial lipopolysaccharides (LPS) on the suppressor activity of mouse spleen cells were examined. Pretreatment with LPS was shown to induce suppressor activity in vivo and in vitro. Concurrent treatment of spleen cells with LPS and imidazole, an agent which increases the activity of cyclic nucleotide phosphodiesterases and hastens the degradation of cyclic AMP, reversed the suppressor-inducing effects of LPS. In vitro treatment of spleen cells with aminophylline, an agent which inhibits phosphodiesterase activity, had no effect on suppressor activity. The reversal of LPS-induced suppressor activity by imidazole was time-dependent and addition of this agent 20 hr after LPS treatment did not reverse suppression. These data are consistent with the hypothesis that LPS-induced suppressor activity may be mediated via cyclic AMP-dependent pathways.