Contrasting mechanisms for suppression of macrophage cytokine release by transforming growth factor-β and interleukin-10

Transforming growth factor (TGF)-β and interleukin (IL)-10 inhibited lipopolysaccharide (LPS)-induced macrophage production of the inflammatory cytokines tumor necrosis factor-α (TNF), IL-1α, and IL-1β by contrasting post-transcriptional mechanisms. TGF-β acted slowly and late, as it required 12-16 h to exert a suppressive effect, and inhibited TNF production even when added 6 h after LPS. TGF-β affected neither the level of TNF mRNA, the release of preformed TNF nor the degradation of TNF. Thus, TGF-β appeared to inhibit translation of TNF mRNA. IL-10 not only suppressed TNF release to a 25-fold greater extent than TGF-β, but also inhibited release of IL-1. In contrast to TGF-β, IL-10 acted on an early step in cytokine production, its effect being maximal 3 h after addition of LPS. Unlike TGF-β, IL-10 markedly suppressed TNF, IL-1α, and IL-1β mRNA levels. However, this was accomplished without suppressing transcription of the corresponding genes. Moreover, cycloheximide antagonized the IL-10-dependent reduction in cytokine mRNA levels. Thus, IL-10 may induce a ribonuclease active on cytokine transcripts or may induce a protein that enhances the susceptibility of TNF, IL-1α, and IL-1β mRNAs to ribonucleolytic action. We conclude that IL-10 and TGF-β induce different phenotypes of macrophage deactivation, and deactivate macrophages by different mechanisms: IL-10 promotes degradation of cytokine mRNA, while TGF-β primarily suppresses translation.