Regulation of IFN-gamma expression in vivo. IFN-gamma up-regulates expression of its mRNA in normal and lipopolysaccharide-stimulated mice.

Immune responses to such stimuli as tissue injury, infection, and allografting result in localized IFN-gamma expression. Autoregulation of cytokine expression has been described for some cytokines in vitro, but whether this occurs in vivo is unknown. We therefore examined the role of murine IFN-gamma in the regulation of its own expression in vivo after stimulation with bacterial LPS. This agent is known to induce IFN-gamma expression in both spleen and kidney in a T cell-independent, cyclosporine-sensitive manner. We found that concomitant administration of a neutralizing mAb to IFN-gamma inhibited not only the MHC expression induced by LPS but also the increased IFN-gamma mRNA expression, suggesting an autoregulatory role for IFN-gamma. Inhibition was dose dependent and observed in both spleen and kidney. The effect was not seen with a neutralizing anti-IL-3 mAb, demonstrating specificity. The inhibition of IFN-gamma mRNA expression by the anti-IFN-gamma mAb occurred in both T cell-deficient athymic nude mice and their normal controls, suggesting that the autoamplification of IFN-gamma mRNA in vivo is T cell independent. Administration of rIFN-gamma to unstimulated mice induced IFN-gamma mRNA expression in spleen and kidney, supporting the conclusion that IFN-gamma up-regulates expression of its mRNA. Exposure of resting murine splenocytes to concentrations of rIFN-gamma as low as 10 U/ml in vitro induced expression of IFN-gamma mRNA. Thus, in vivo IFN-gamma may participate in an autoregulatory loop to amplify the amount of IFN-gamma expressed both at the site of local inflammation and at remote sites. This would have relevance in the mechanism by which the host defends itself against and prevents dissemination of an infectious agent.