Cell surface antigens of the major histocompatibility complex (MHC) play a crucial role in the initiation of immune reactions. To investigate whether the expression of MHC antigens on pancreatic islet cells could be altered, we have cultured mouse islets in the presence of interferon-γ (IFN-γ) and subsequently examined the levels of MHC antigen by indirect immunofluorescence using monoclonal antibodies. IFN-γ induced a 10-fold increase in H-2K antigen expression on islet cells, the percentage of cells with detectable H-2K expression increasing from 24% to 98%. The effects of IFN-γ on H-2D and la antigen expression were less marked, with only a twofold increase in mean fluorescence levels, the percentage of cells with detectable levels ofexpression increasing from 10% to 48% and 5% to 16%, respectively. Using double-indirect immunofluorescence, it was demonstrated that IFN-γ enhanced expression of H-2K and H-2D antigens on β-cells. However la-positive-cells were undetectable in the presence or absence of IFN-γ.

The ability of IFN-γ to induce increased expression of H-2 antigens on β-cells may represent a mechanism for targeting immune (cytotoxic) reactions to β-cells, e.g., in autoimmune insulitis or allograft rejection.

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