Renal allograft rejection: protection of renal epithelium from natural killer cells by cytokine-induced up-regulation of class I major histocompatibility antigens.

The potential of natural killer (NK) cells to contribute to renal allograft rejection was modelled by mixing NK cells with cultured renal epithelial cells. It was found that the renal cells were readily lysed by cytokine-activated NK cells. Renal cells which were previously stimulated by culture with either interferon-gamma (IFN-gamma) or supernatant from mixed leucocyte cultures (MLC) were relatively resistant to such lysis; stimulation with tumour necrosis factor-alpha (TNF-alpha) had no effect. None of these cytokine preparations had any effect on the lysis of renal cells by either specific cytotoxic T lymphocytes or the antibody-dependent cell-mediated cytotoxic mechanism. The expression of class I major histocompatibility complex (MHC) antigens was up-regulated by stimulation of renal cells with either IFN-gamma or MLC supernatant; treatment with TNF-alpha had no effect on the expression of these antigens. Protection from NK cell-mediated lysis appeared to correlate with the expression of class I MHC antigens by the renal cells. Artificial removal of these MHC antigens by treatment with citric acid significantly increased the susceptibility of cytokine-stimulated renal cells to lysis by activated NK cells. This increase was not caused by enhanced binding of NK cells to acid-treated renal cell targets. These results suggest that high levels of class I MHC antigen expression block NK cell triggering after engagement with renal epithelial cells. It is concluded that cytokines present within the renal microenvironment during rejection protect graft cells from lysis by NK cells by causing local upregulation of the expression of class I MHC molecules.