Differently, the in vivo antibacterial efficacy of LL-37 was mostly lost at longer-term (Fig. 5b), probably due to its higher susceptibility to proteases29. This is in contrast with previous findings by Beagumont and colleagues showing that in a murine model of acute P. aeruginosa lung infection, LL-37 enhanced bacterial clearance in vivo only over 24 hours, by means of neutrophils recruitment, while no effect was obtained 6 hours after infection47. However, in their work, bacteria and peptide were co-administered via intranasal instillation rather than intra-tracheally. This latter administration route provides a more direct introduction of bacteria into the lungs and a more reproducible infection that can be more representative of pneumonia, generally leading to establishment of infection in the lower regions of the lungs48. In addition, intra-tracheal administration of a drug better mimics an aerosol-based therapy. Furthermore, immediate administration of LL-37 following bacterial inoculation as used in the paper47 did not allow sufficient time for the bacteria to adapt to the lung microenvironment before being exposed to LL-37. Note that this previously used experimental procedure could not provide a valuable indication of the antimicrobial effectiveness of AMPs in vivo. Thus, in this study, we purposely delayed the AMP administration at 2 hours after bacterial infection to better reflect the real life infectious conditions.