Infection with an MCMV containing the model epitope OVA257-264 (SIINFEKL) inserted in the M45 protein (MCMV-M45-SIINFEKL) resulted also in an antigen-specific T cell response that depended on B7-mediated costimulation (Figure 3C), indicating that non-viral epitopes elicit similar costimulation dependent responses. This evidence concerns the gene CD80 and infection.