Direct evidence that interferon-beta mediates enhanced HLA-class I expression in measles virus-infected cells.

Viral infection results in enhancement of HLA-class I expression in a number of cell types, including glial cells, which normally do not express these molecules. This enhancement may occur through a direct interaction between a viral component and the HLA-class I gene or indirectly through virus-induced soluble factors produced by infected cells. These include cytokines such as IFN-gamma, IFN-alpha/beta, and TNF-alpha, known to enhance class I expression. Measles virus (MV) infection of a human glioma cell line (U-105 MG) and of primary human umbilical vein endothelial cells enhances the expression of HLA-class I molecules on these cells. The enhancement of HLA-class I is dependent on infectious virus, as antibody-neutralized MV has no effect on class I expression. In this study, we demonstrate the presence of an HLA-class I-enhancing factor in supernatants from MV-infected cells. The supernatant class I-enhancing factor is not IFN-gamma, IFN-alpha, or TNF-alpha because MV-infected cells did not produce measurable levels of these cytokines as detected by immunoassay or polymerase chain reaction. In contrast, IFN-beta is produced by the infected cells and the supernatant class I-enhancing factor could be entirely neutralized by antibodies to IFN-beta, but not antibodies to IFN-alpha, TNF-alpha, or non-immune sera. Furthermore, preincubation of cells with neutralizing antibodies to IFN-beta prior to infection blocked MV enhancement of HLA-class I completely in the U-105 MG cells and by as much as 74% in the umbilical vein endothelial cells. The results of these experiments provide direct evidence that enhanced HLA-class I expression in MV-infected cells is mediated primarily by IFN-beta.