IL-10 inhibits transcription of cytokine genes in human peripheral blood mononuclear cells.

Upon addition of LPS to human PBMCs, IL-1 beta, IL-6, and TNF-alpha were released in the culture media in a time-dependent manner. Cytokine release began 2 h after LPS addition and maximal release of all three cytokines was observed between 6 and 8 h. Northern analysis revealed that, for each cytokine, mRNA accumulation preceded protein release. When added either 2 h before or at the same time as LPS, IL-10 inhibited both the cytokine release and mRNA accumulation almost completely. Similar inhibition was observed when IL-10 was added 2 h after LPS, a time point that coincided with the onset of the rapid burst of cytokine mRNA accumulation. The inhibitory activity of IL-10 was abrogated by cycloheximide, suggesting an involvement of newly synthesized proteins in IL-10 action. By using nuclear run-on transcription assays, we have found that IL-10 inhibited transcription of all three cytokine genes in LPS-stimulated PBMCs. In contrast, IL-10 moderately enhanced degradation of IL-6 mRNA, but not of mRNAs for IL-1 beta and TNF-alpha. Thus, the present study provides the first evidence that, in human PBMCs, IL-10 inhibits cytokine synthesis by acting mainly at the level of cytokine gene transcription.