Down regulation of murine MHC class I expression by bovine herpesvirus 1.

The objective of this study was to investigate the effect(s) of bovine herpesvirus 1 (BHV-1) infection on the expression of MHC class I molecules in murine fibroblasts. L-cells were infected with BHV-1 at a multiplicity of infection (m.o.i.) of 10 plaque forming units (PFU) per cell, and the expression of MHC class I molecules was analyzed by flow cytometry and immunoprecipitation. Temporal studies revealed a reduction in class I expression beginning at 8 h post infection (p.i.) which reached a maximum between 10 to 16 h p.i. The loss of class I expression was restored in the presence of phosphonoacetic acid (30 micrograms/ml), a late herpesviral protein synthesis inhibitor. However, addition of cycloheximide, a total protein synthesis inhibitor (100 micrograms/ml), did not result in any difference in class I expression between virus-infected and mock-infected cells. These results suggest that the reduced class I expression is a direct consequence of BHV-1 infection, and that the late viral gene product(s) may be involved in this process. Similar phenomena may occur in natural BHV-1 infection in cattle, and this may be one of the mechanisms of immune suppression by BHV-1.