(A) Total protein content and LDH levels in the BAL samples of mice infected with PA or SP at day 3 or 7 post-MHV infection and their respective histological analyses (B) indicated increased tissue injury in the superinfection group. Mouse survival was measured to compare the effect of MHV infection on host survival post-PA or SP infections (C). Data are pooled from two independent experiments for each survival curve. N = 11 each group for PA and 8–9 for SP. *, P <0.05, **, P < 0.01, ****, and P < 0.001 using one-way ANOVA followed by Dunnett’s multiple comparisons test. Survival curves were compared using Log-rank (Mantel-Cox) test.