Enhancement of class I HLA antigen expression by cytomegalovirus: role in amplification of virus infection

We have investigated the effect of cytomegalovirus (CMV) infection on the expression of class I HLA antigens on fibroblasts in vitro. Scanning and integrating microdensitometry was used to quantitate the level of cytoplasmic class I antigen expression, and an antibody binding assay was used to quantitate cell surface expression of class I HLA molecules. CMV infection resulted in a significant increase in the level of cytoplasmic and cell surface class I HLA antigen expression of fibroblast monolayers. The maximal effect was seen at 72 hours postinfection and was observed with both the laboratory strain of CMV, strain AD169, and with CMV purified directly from clinical specimens. Part of the increased HLA expression was mediated by interferon released from infected cells; however, an additional direct effect of the virus itself has not been ruled out. Interferon-induced increased expression of class I HLA antigens was accompanied by increased binding of CMV to the cells, consistent with our recent demonstration that class I HLA molecules can function as a cellular receptor for CMV.