Subtherapeutic corticosteroids potentiate the ability of interleukin 10 to prevent chronic inflammation in rats

Background and Aims: Interleukin (IL)-10, which inhibits macrophages and T-helper lymphocyte type 1 (TH₁) lymphocytes, attenuates chronic granulomatous inflammation induced by bacterial cell wall polymers. This study determines whether corticosteroids enhance the protective effects of IL-10 in cultured peripheral blood mononuclear cells (PBMNCs) and in vivo when started before or after the onset of experimental chronic granulomatous inflammation. Methods: Intestines of Lewis rats were injected intramurally with streptococcal peptidoglycan-polysaccharide (PG-APS) polymers. Daily murine recombinant IL-10 and/or dexamethasone (DEX) therapy was started 12 hours before or at several intervals after PG-APS injection. Results: IL-10 plus corticosteroids additively inhibited IL-1β secretion in human PBMNCs but preserved the beneficial IL-1RA/IL-1β ratio induced by IL-10. IL-10 started before PG-APS injection significantly attenuated intestinal and extraintestinal inflammation, with even more pronounced effects in combination with subtherapeutic doses of DEX. The combination of DEX decreased the effective dose of IL-10 by at least one half. After onset of systemic inflammation using doses effective for prevention, IL-10 monotherapy had nearly no benefit and DEX plus IL-10 was similar to the mild therapeutic effect of DEX alone. Conclusions: The combination of IL-10 and corticosteroids allows lower doses of both agents in preventing chronic intestinal and systemic inflammation. However, timing of IL-10 administration is a critical variable in regulating inflammation.