Fig. 6: Interaction between epithelial CD47 and bacterial FnBP is essential to cause super-infection.

a–j 6–8-weeks-old (18–21 g of body weight) FoxJ1-Cre; floxed (Cd47^Foxj1) and control floxed (Cd47^f/f) mice were infected with 100 PFU of influenza virus on day 0, and 1 ×10⁸ CFU of S. aureus WT (FnBP A+/B+) and double deletion mutant (FnBP A–/B–) on day 7 (Cd47^f/f + FnBP A+/B+, n = 9; Cd47^f/f + FnBP A–/B–, n = 11; Cd47^Foxj1 + FnBP A+/B+, n = 12; Cd47^Foxj1 +FnBP A–/B–, n = 10). Body weight loss (a) and survival rates (b) were monitored for 29 days. The dotted line indicates the body weight exclusion cut-off. A mantel cox survival analysis was used to compare the survival rates between groups. The numbers within circles or squares represent the count of surviving mice. Representative hematoxylin and eosin (H&E) staining of lung sections (c). Lung injury scores are presented as violin plots (Cd47^f/f + FnBP A+/B+, n = 4; Cd47^f/f + FnBP A–/B–, n = 5; Cd47^Foxj1 + FnBP A+/B+, n = 5; Cd47^Foxj1 +FnBP A–/B–, n = 5). Tissue injury parameters were measured at 24 h after bacterial infection (Cd47^f/f + FnBP A+/B+, n = 4; Cd47^f/f + FnBP A–/B–, n = 5; Cd47^Foxj1 + FnBP A+/B+, n = 5; Cd47^Foxj1 +FnBP A–/B–, n = 5); total cell number in BAL fluids (BALF) (d), bacterial adherence (e) and invasion (f) in the lung, and bacterial burden in the spleen (g), total protein concentrations in BALF (h), and inflammatory cytokines TNF-α (i) and IL-6 (j) in BALF. k Proposed model of viral infection-induced CD47-mediated secondary bacterial infection. Data are presented as mean values ± SEM. Significance was determined by one-way ANOVA with Tukey’s multiple comparisons test. Source data are provided as a Source Data file.