The study shows that the natural antimicrobial peptide LL‑37 can kill certain lung‑related bacteria, but the lung’s own surfactant can dampen its effect unless you use a fairly high dose. A related peptide, PF‑18, is even more blocked by surfactant at low doses. At very high concentrations, both peptides work better and don’t mess up the surfactant’s surface properties.

The antibacterial activities of the cathelicidin peptides LL-37 and an 18-residue C-terminal fragment of prophenin, corresponding to positions 62 to 79 of native prophenin (PF-18), were analyzed in the presence of a modified surfactant preparation isolated from minced porcine lungs. At low micromolar concentrations, both LL-37 and PF-18 showed significant activities against different serotypes of group B streptococci, with LL-37 being more active on a molar basis. The surfactant preparation at a concentration of 10 mg/ml partly blocked the antibacterial activity of 9 microM LL-37 and completely blocked the antibacterial activity of 9 microM PF-18. However, 10 mg of the surfactant preparation per ml had only minor inhibitory effects on LL-37 and PF-18 at 90 microM. Addition of up to 900 microM PF-18 did not affect the surface properties of the surfactant preparation. These data suggest that surfactant preparations containing antimicrobial peptides could be useful for the local treatment of pulmonary infections.