Perforin-dependent CD4+ T-cell cytotoxicity contributes to control a murine poxvirus infection.

CD4(+) T cells are generally regarded as helpers and regulators of the immune response. Although cytolytic CD4(+) T cells have been described, whether those generated during the course of a viral infection play a role in virus control remains unknown. Here we show that during acute infection with ectromelia virus, the mouse homolog of the human virus of smallpox, large numbers of CD4(+) T cells in the draining lymph node and liver of resistant mice have a cytotoxic phenotype.