Latent infection with MuHV-4 enhances NK-cell degranulation and cytotoxicity. (A) Latent infection with MuHV-4 increases NK-cell degranulation. Peritoneal cells from mock, O73.stop, or MuHV-4 latently infected mice were cultured ex vivo with YAC-1 target cells at the indicated target:effector ratios for 2 hours, followed by flow cytometric analysis of CD107a expression on the surface of NK1.1⁺CD3⁻ NK cells. Control mice were incubated without targets. Bars represent the mean ± SD of 5 to 10 mice per group. *P < .032 (MuHV-4 compared with mock or O73.stop). These data are representative of 2 independent experiments with 15 to 20 total mice per condition. (B) Latent infection with MuHV-4 induces cytotoxic activity by NK cells. Peritoneal cells from control (naive) mice and mice infected 28 days previously with MuHV-4 were enriched for NK cells and then coincubated with RMA-S target cells for 4 hours at the indicated effector:target ratios before analysis of target cell death by 7-AAD. *P < .003 (MuHV-4 vs control). These data are representative of 2 independent experiments with 20 to 30 mice per group per experiment.