Immune Responses in Interleukin-2-Deficient Mice

The role of costimulatory signals m T cell induction was evaluated in mice lacking the interleukm-2 (IL-2) gene. In vitro secondary antiviral T cell responses were absent unless IL-2 was added, confirming the crucial role of IL-2 m vitro. In vivo, primary and secondary cytotoxic T cell responses against vaccinia and lymphocytic choriomeningitis virus were within normal ranges. B cell reactivity to vesicular stomatitis virus was not impaired. T helper cell responses were delayed but biologically functional. Natural killer cell activity was markedly reduced but reducible. These normal in wvo immune responses in IL-2-deficient mice question the importance of IL-2 as defined by in vitro studies.