CD4 T cells maintain cytotoxic activity in the absence of IFN-γ. A, Experimental design of the in vivo cytotoxicity assay. IFN-γ neutralization was confirmed by ELISA. Forty hours after target cell transfer, recipient mice were sacrificed, and the percentage-specific lysis was calculated as described in Materials and Methods. B, Bar diagram showing the percentage of specific lysis after in vivo IFN-γ neutralization or isotype control treatment. C, Bar diagram shows the percentage of specific lysis of long-term infected IFN-γ−/− mice relative to long-term infected wild-type controls. Error bars represent SD.