Keratinocyte expression of class II antigens (HLA-DR, human; Ia, murine) is associated with certain cutaneous diseases, especially those marked by the infiltration of immune and inflammatory cells into the skin. It has been shown that interferon-gamma (IFN-gamma) is capable of inducing human keratinocytes to express HLA-DR. Similar results, however, have not been duplicated in murine systems. The purpose of this study was to determine whether IFN-gamma was capable of inducing murine keratinocyte expression of Ia in vivo in an experimental model in which epithelial cells in a variety of organs were shown to express Ia after the i.v. injection of IFN-gamma. Recombinant murine IFN-gamma was injected into BALB/c mice. Biopsies of skin and intestine were analyzed by indirect immunoperoxidase to identify Ia-expressing keratinocytes and mucosal cells, respectively. Interferon-gamma was administered as either: 1) a single s.c. injection, 2) multiple i.v. injections of increasing doses (10(3)-10(5) U/d) on 3 consecutive d, or 3) i.p. injections of 5 X 10(4) U/d or 5 X 10(5) U/d on 6 consecutive d. At all i.v. and i.p. injection doses, the intestinal villi mucosal cells were induced to express Ia. Keratinocyte expression of Ia, however, was observed only in animals that received the two higher i.p. doses. Procedures to augment Ia expression, e.g., combined treatment with pertussis toxin, dinitrofluorobenzene, tumor necrosis factor, and indomethacin, did not enhance the ability of IFN-gamma to induce keratinocyte expression of Ia. We conclude that: 1) high doses of IFN-gamma are required to induce murine keratinocyte Ia expression in vivo and 2) low doses of IFN-gamma, although capable of inducing intestinal mucosal cells to express Ia, do not induce keratinocyte Ia expression.