FIG 1.

A 6-h delay between primary infection and superinfection allows robust superinfection exclusion. The indicated mammalian cell lines were infected with rPR8 virus and were simultaneously (0hr) or sequentially (6hr) infected with rH3N2 virus; all infections were performed at MOI = <0.3 TCID₅₀/cell. (A) Representative fluorescence-activated cell sorter (FACS) plots showing expression of H1 versus H3 within MDCK cells. (B) H3⁺ frequencies within H1⁺ cells following simultaneous or sequential infection, in the indicated cell lines. The values for both the 0-h and 6-h groups are shown as percentages of the mean values of the 0-h control group to clearly illustrate the percentages of reduction in cellular susceptibility in the 6-h group. Data are presented as means (n = 3 cell culture wells) ± standard deviations. ***, P < 0.001; ****, P < 0.0001 (t test).