Cutting edge: MHC class II-restricted killing in vivo during viral infection.

Class II-restricted CD4 T cell-mediated killing of target cells has previously been documented in vitro but not in vivo. In this study, we demonstrate CD4-dependent MHC class II-restricted killing in lymphocytic choriomeningitis virus-infected mice in vivo using an in vivo cytotoxicity assay that features class II-expressing B cells as targets.