The C protein of measles virus inhibits the type I interferon response

Type I interferons (IFNα/β) are an important part of innate immunity to viral infections because they induce an antiviral response and limit viral replication until the adaptive response clears the infection. Since the nonstructural proteins of several paramyxoviruses inhibit the IFNα/β response, we chose to explore the role of the C protein of measles virus (MV) in such inhibition. Previous studies have suggested that the MV C protein may serve as a virulence factor, but its role in the pathogenesis of MV remains undefined. In the present study, a recombinant MV strain that does not express the C protein (MV C−) and its parental strain (Ed Tag) were used. Growth of MV C− was restricted in human peripheral blood mononuclear cells and HeLa cells, but in the presence of neutralizing antibodies to IFNα/β, MV C− produced titers that were equivalent to those of Ed Tag. In addition, expression of the MV C protein from plasmid DNA inhibited the production of an IFNα/β responsive reporter gene and, to a lesser extent, inhibited an IFNγ responsive reporter gene. The ability of the MV C protein to suppress the IFNα/β response was confirmed using a biologic assay. After IFNβ stimulation, HeLa cells infected with Ed Tag produced five-fold less IFNα/β than cells infected with MV C−. While the mechanism of inhibition remains unclear, these data suggest that the MV C protein plays an important role in the pathogenesis of MV by inhibiting IFNα/β signaling.