Induction of HLA class I mRNA by cytokines in human fibroblasts: comparison of TNF, IL-1 and IFN-β

Abstract

Expression of HLA class I antigens is known to be regulated by various cytokines at both the mRNA and protein levels. We have examined the induction of HLA-B7 by tumor necrosis factor α (TNF), interleukin 1α (IL-1) and interferon β (IFN-β) in normal human diploid FS-4 fibroblasts. Optimal induction of HLA-B7 by TNF at 24 h was shown to require a continuous presence of TNF. Since TNF also induces IFN-β in these cells and the latter cytokine itself has the capacity to upregulate HLA class 1 expression, we investigated the role of autocrine IFN-β in the induction of HLA-B7 by TNF. Experiments with neutralizing polyclonal antibodies to recombinant IFN-β showed that the induction of HLA-B7 mRNA by TNF was partially dependent on autocrine IFN-β. However, TNF and IFN-β induced HLA-B7 mRNA with similar kinetics and treatment with saturating concentrations of both TNF and IFN-β resulted in an additive or possibly synergistic response. The latter findings support the idea that induction of HLA class I by TNF is not mediated solely by autocrine IFN-β produced in response to TNF. In addition, experiments with the protein synthesis inhibitor cycloheximide suggested that the induction of mRNAs for both the heavy and light (β 2-microglobulin) chains of the HLA class I antigen by TNF did not require de novo protein synthesis. IL-1 was also shown to increase steady-state mRNA levels of HLA-B7 with kinetics similar to those of TNF and IFN-β in FS-4 cells. Our data suggest that TNF stimulates gene expression of the HLA class I antigens through multiple mechanisms. Although one pathway of induction apparently involves autocrine IFN-β, available evidence suggests that de novo synthesis of IFN-β (or of some other protein) in response to TNF is not an important step in HLA-B7 induction. Rather, the slow kinetics of HLA-B7 induction by TNF can be explained by the need for a gradual and progressive accumulation of the activating signal(s) generated by TNF.