Interleukin-1-like activity in normal rat skin after in vivo treatment with interferon-gamma

The influence of interferon-gamma (IFN-gamma) on immune responses is still ambiguous. We have investigated whether IFN-gamma influences the constitutive interleukin-1 (IL-1)-like activity in normal rat skin because IL-1 is a regulatory cytokine in immune responses. Rats were injected intradermally into both ears with different doses of rat recombinant IFN-gamma (10(3)-10(5) U), and control animals were given phosphate-buffered saline (PBS). The animals were killed at different times and the ears were cut off at the bases. The biologic activity of the IFN-gamma was verified by immunohistochemistry on injected ears, showing a time- and dose-dependent induction of major histocompatibility complex class II antigens on the keratinocytes. Aqueous extracts of homogenized ear skin were tested for IL-1-like activity in a mouse thymocyte bioassay. No major effects of IFN-gamma on the constitutive IL-1-like activity in the rat skin were found; at 6 h there was a slight reduction and at 72 h an increase in IL-1 bioactivity in extracts from IFN-gamma (10(5) U)-injected animals compared with PBS-treated controls (p less than 0.05). We conclude that the regulation of immune responses in the rat skin by IFN-gamma is less likely to be mediated via changes in the IL-1-like activity.