Antimicrobial Peptide Omiganan Enhances Interferon Responses to Endosomal Toll‐Like Receptor Ligands in Human Peripheral Blood Mononuclear Cells

LL‐37 is a cationic antimicrobial peptide and the sole human member of cathelicidins. Besides its bactericidal properties, LL‐37 is known to have direct immunomodulatory effects, among which enhancement of antiviral responses via endosomal toll‐like receptors (TLRs). Omiganan pentahydrochloride is a synthetic cationic peptide in clinical development. Previously, omiganan was primarily known for its direct bactericidal and antifungal properties. We investigated whether omiganan enhances endosomal TLR responses, similar to LL‐37. Human peripheral blood mononuclear cells were treated with endosomal TLR3, −7, −8, and −9 ligands in the presence of omiganan. Omiganan enhanced TLR‐mediated interferon‐α release. Subsequent experiments with TLR9 ligands showed that plasmacytoid dendritic cells were main contributors to omiganan‐enhanced IFN production. Based on this type I interferon‐enhancing effect, omiganan may qualify as potential treatment modality for virus‐driven diseases. The molecular mechanism by which omiganan enhances endosomal TLR responses remains to be elucidated.