INTERACTIONS BETWEEN INTERFERON-GAMMA AND RETINOIC ACID WITH TRANSFORMING GROWTH-FACTOR-BETA IN THE INDUCTION OF IMMUNE RECOGNITION MOLECULES

The cell-surface expression of major histocompatibility (MHC) antigens and the adhesion molecule intercellular adhesion molecule1 (ICAM-1) i s essential for target cell recognition by T lymphocytes. The expressi on of both classes of molecule is induced by various cytokines, notabl y interferon gamma (IFNgamma). Since transforming growth factor beta ( TGFbeta) has been recently reported to antagonise HLA-DR induction by IFNgamma we have examined, using a number of murine and human cell lin es, the effect of TGFbeta on IFNgamma-induced MHC class I and class II and ICAM-1 expression. All of the cell lines tested expressed elevate d class I MHC following IFNgamma treatment. Class II MHC induction was seen on most but not all of the cells, the exceptions being among a p anel of human colorectal carcinoma cell lines. A striking difference b etween cells of different origin was noted in the response to TGFbeta. TGFbeta was found to antagonise IFNgamma-induced class I and class II MHC expression on C3H 10T1/2 murine fibroblasts, early-passage BALB/c mouse embryo fibroblasts, a murine oligodendroglioma cell line, and o n MRC5 human fibroblasts and two human glioblastoma cell lines. Class II MHC was much more strongly inhibited (sometimes completely) than cl ass I MHC. TGFbeta also inhibited induction of class I MHC expression by IFNalpha. However, TGFbeta did not inhibit class I or class II MHC induction by IFNgamma in any of the nine colorectal carcinoma cell lin es, although two of five of the lines tested were growth-inhibited by TGFbeta. On the other hand, human ICAM-1 induction by IFNgamma was not affected by simultaneous treatment with TGFbeta in any of the cell li nes. The down-regulation of IFNgamma-induced MHC antigens by TGFbeta i s not, therefore, the result of a general antagonism of IFNgamma. Reti noic acid has recently been reported to induce ICAM-1 expression on hu man tumour cells. We have confirmed this observation on MRC5, and the two human glioblastoma cell lines, however six colorectal carcinoma ce ll lines tested did not respond. In contrast to IFNgamma-induced ICAM- 1 expression, retinoic-acid-induced ICAM-1 expression was inhibited by TGFbeta on two of the three responsive lines.