In order to explore the importance of CD4+ T cell derived Prf1 for successful host defense in CNS virus infection in vivo, we immunized Prf1 deficient mice (Prf1-/-) with MVA/CFA and established viral encephalitis in CD8+ T cell depleted animals by intrathecal infection with VV (Figure 8). This evidence concerns the gene PRF1 and viral infectious disease.