IAV infection of WT and Tg-FcγRIIA mice. WT and Tg-FcγRIIA mice were infected intranasally with 25 µL of PBS (control) or 25 µL of PBS containing a sublethal dose of IAV H3N2. Forty-eight days later, mice were inoculated intranasally with 5 LD50 of IAV H1N1. Mouse weight (A), body temperature (B), and survival (C) were recorded every day for 9 days. N = 8 mice per group. (D-E) WT and Tg-FcγRIIA mice were injected intranasally with 25 µL of PBS (control) or 25 µL of PBS containing a sublethal dose of IAV H1N1. Sixty-eight days later, mice were inoculated intravenously with 108 TCID50 of heat-inactivated IAV H1N1 (to induce the formation of immune complexes). At the indicated periods of time, venous blood was collected and incubated with allophycocyanin (APC)-labeled anti-CD41 or matched isotypic controls. The percentages of circulating platelets (CD41+) measured at each indicated time point were determined by quantitative flow cytometry using their respective group measured at T = 0 as relative controls. Data are mean ± SEM; N = 7-8 mice per time point. **P < .001; ***P < .0001; NS, nonsignificant.
