Flavivirus infection up-regulates the expression of class I and class II major histocompatibility antigens on and enhances T cell recognition of astrocytes in vitro

West Nile virus (WNV) infection of astrocytes can up-regulate their expression of both class I and class II major histocompatibility complex (MHC) antigens as determined by flow cytometry with monoclonal antibodies specific for class I and class II MHC antigens. The up-regulation of class I MHC antigen expression could be partly caused by interferon secreted after WNV infection because the synthetic interferon inducer polyinosinic-polycytidylic acid (poly I : C) has similar effects. In contrast the up-regulation of class II MHC antigen expression was not induced by poly I : C. The increased MHC antigen expression by WNV infection had significant effects on T cell recognition. Thus, WNV and influenza virus A/WSN double-infected astrocytes but not astrocytes infected by A/WSN alone were lysed by influenza virus-immune cytotoxic T cells. Similarly, WNV-infected astrocytes were better stimulators than normal astrocytes for a class II MHC-reactive T cell line, both in terms of T cell proliferation and interleukin release.