The antimicrobial peptide LL-37 modulates the inflammatory and host defense response of human neutrophils

Background and Aim: LL-37 is a human cathelicidin antimicrobial peptide and acts as effector molecule of the innate immune system with direct antimicrobial and immunomodulatory effects. The aim of this study was to test whether cathelicidin modulates the response of neutrophils to microbial stimulation and improves their bactericidal activity.

Material and Methods: Human neutrophils were isolated from human buffy-coat and stimulated with LPS, Staphylococcus aureus and Pseudomonas aeruginosa following preincubation with different concentrations of LL-37, then cytokine production was measured by ELISA. Also ROS production of neutrophils was determined by the luminometeric method and flow cytometric methods. Peritoneal mouse neutrophils isolated from CRAMP deficient and wildtype animals were treated with LPS and TNF-a in the supernatant was measured by ELISA. Antimicrobial activity of neutrophils was detected by incubating neutrophils isolated from CRAMP knockout and wildtype mice with bacteria and the antimicrobial activity was determined.

Results: Preincubation with LL-37 significantly decreased the release of proinflammatory cytokines from human neutrophils stimulated with TLR ligands or whole bacteria and this action was dose-dependent. The production of ROS induced by PMA was significantly amplified in presence of LL-37 and was dose-dependent. Neutrophils from CRAMP deficient mice released significantly more TNF-a after LPS stimulation and showed decreased antimicrobial activity as compared to neutrophils from wildtype animals.

Conclusion: LL-37 modulates in the dose-dependent manner the response of neutrophils to activation by microbial patterns. Endogenousely produced cathelicidin is sufficient for this effect. Cathelicidin controls the release of inflammatory mediators while increasing antimicrobial activity of neutrophils.