To study whether upon viral infection CD4- or Ncr1-specific IFN-γ gene reconstitution affects systemic IFN-γ levels, WT, IFN-γOFF, IFN-γCD4-ON and IFN-γNcr1-ON mice were intravenously (i.v.)infected with 2 x 106 pfu vaccinia virus (VACV), serum samples were drawn at the indicated time points, and IFN-γ protein levels were determined by an ELISA method. Here, IFNG is linked to viral infectious disease.