FIG. 4.

RSV-induced NK cytotoxicity is perforin dependent. Seven days p.i., BAL samples from TLR4^null (open bar) and TLR4^wt (closed bar) mice were examined following RSV infection. Samples were purified for NK cells (DX5⁺) (80 to 90% enrichment) by positive selection using the MACS separation system. NK lytic activity against YAC-1 target cells was assessed in the presence or absence of EGTA-MgCl²⁺ at effector-to-target ratios of 40:1 (presented), 20:1, 10:1, and 5:1 (data not shown). The asterisk indicates a significant difference (P < 0.05) between TLR4^null and TLR4^wt mice. The results are representative of two independent experiments.