IFN-gamma is a prerequisite for optimal antigen processing of viral peptides in vivo.

The immediate early protein pp89 of mouse CMV is processed into the nonapeptide YPHFMPTNL, which is presented to CD8+ T lymphocytes by the H-2 Ld molecule. The tissue distribution of this peptide was determined during the course of mouse CMV infection. In tissues, there was no general correlation between peptide processing and infectious virus productivity. Immunosuppression by sublethal irradiation resulted in enhanced MCMV replication but did not increase the peptide yield and drastically reduced the peptide to plaque-forming unit rate in infected organs. IFN-gamma administration restored efficient peptide processing in the immunocompromised host, and neutralization of IFN-gamma in the immunocompetent host decreased peptide processing. This suggests that the efficiency of peptide processing after CMV infection in vivo is governed by IFN-gamma rather than by the productivity of virus infection.