(A) Schematic of Z-VAD-FMK treatment of neonatal ALI cultures. Z-VAD-FMK (40 μM) was applied in the bottom chamber 2 hours prior to RSV infection until the assays performed at 6 hpi and 2 dpi in B–E. (B) Relative levels of RSV L gene at 6 hpi by RT-qPCR. (C) Representative double staining for RSV F (green) and c-Casp-3 (red) at 2 dpi. Blue color is nucleus staining and the overlay of red, green, and blue shows as pink color. (D) Relative levels of RSV L gene at 2 dpi by RT-qPCR. (E) Relative abundances of RSV F⁺ and c-Casp-3⁺ cells at 2 dpi quantified from double stained images. (F) Schematic of RSV-GFP infection (1 × 10⁶ pfu) of infant hPCLSs pretreated with vehicle or Z-VAD-FMK (40 μM) 2 hours prior to infection. (G) Representative images of RSV-GFP (green) and c-Casp-3 (red) staining in control and Z-VAD-FMK–treated infant hPCLSs. The contour of RSV-GFP⁺ cells was outlined in panels showing enlarged areas. Blue color is nucleus staining and the overlay of red, green, and blue shows as pink color. Solid lines mark basement membrane and dotted lines mark the enlarged areas. (H) Relative abundance of RSV-GFP⁺ cells and RSV⁺c-Casp-3⁺ cells in bronchial epithelium of infant hPCLSs. Each dot represents quantification of 1 airway. A total of 9 airways from 2 donors, 4–5 airways per donor, were quantified. Each dot (except for panel H) represents 1 donor. Bar graphs represent mean ± SEM. Statistical significance was calculated by 2-tailed Student’s t test in B, D, E, and H. Solid lines mark basement membrane. **P < 0.01, ***P < 0.001. Scale bar: 50 μm.