SUPPRESSION OF TUMOR-NECROSIS-FACTOR-ALPHA PRODUCTION BY INTERLEUKIN-10 IS ENHANCED BY CAMP-ELEVATING AGENTS

The pro-inflammatory peptide tumor necrosis factor-alpha (TNF) stimula tes production of the anti-inflammatory cytokine interleukin-10 by mon ocytes which in turn inhibits the synthesis of TNF. This inhibitory ef fect of interleukin-10 may contribute to the balance of pro- and anti- inflammatory cytokines in several diseases, e.g., chronic inflammatory bowel disease. In the present study we addressed the question whether interleukin-10 in combination with other TNF-suppressing agents leads to enhanced suppression of TNF synthesis. We investigated the inhibit ory potency of interleukin-10 in combination with rolipram, a specific type IV phosphodiesterase inhibitor, or with cicaprost, a stable pros tacyclin analogue in lipopolysaccharide-stimulated human peripheral bl ood mononuclear cells. Peripheral blood mononuclear cells were stimula ted with 10 ng/ml lipopolysaccharide in the absence or presence of int erleukin-10 or one of the cAMP-elevating agents. First, we confirmed t he TNF-suppressing effect of interleukin-l0, rolipram and cicaprost al one and determined the IC50 for these substances. Second, for the comb ination of interleukin-l0 with one of the cAMP-elevating substances we were able to demonstrate enhanced TNF inhibition. Of these, the combi nation of interleukin-l0 and rolipram revealed an additive effect. The maximal TNF synthesis of 5.5 +/- 1.1 ng/ml after lipopolysaccharide s timulation alone was inhibited by 0.1 ng/ml interleukin-l0 to 2.7 +/- 0.6 ng/ml TNF and by 100 nM rolipram to 3.1 +/- 0.6 ng/ml TNF. Both su bstances combined suppressed TNF synthesis to 1.5 +/- 0.3 ng/ml. After stimulation with Staphylococcus epidermidis we could demonstrate a mo re pronounced inhibition of TNF synthesis by interleukin-l0 compared t o rolipram which was more effective after stimulation with lipopolysac charide. Finally, the additive inhibitory effect of interleukin-l0 and rolipram could be confirmed on the level of TNF mRNA. The results obt ained in the present investigation could form a prerequisite to study the combination of interleukin-l0 and cAMP-elevating agents in in vivo models of acute or chronic inflammatory diseases.