d-enantiomers of CATH-2 enhance the response of macrophages againstserotype 2.

INTRODUCTION: Due to the increase of antibiotic resistant bacterial strains, there is an urgent need for development of alternatives to antibiotics. Cathelicidins can be such an alternative to antibiotics having both a direct antimicrobial capacity as well as an immunomodulatory function. Previously, the full d-enantiomer of chicken cathelicidin-2 (d-CATH-2) has shown to prophylactically protect chickens against infection 7 days post hatch when administeredthree days before hatch. OBJECTIVES: To further evaluate d-CATH-2 in mammals as a candidate for an alternative to antibiotics.In this study, the prophylactic capacity of d-CATH-2 and two truncated derivatives, d-C(1-21) and d-C(4-21), was determined in mammalian cells. METHODS: Antibacterial assays; immune cell differentiation and modulation; cytotoxicity, isothermal titration calorimetry;prophylactic capacity of peptides in aninfection model. RESULTS: d-CATH-2 and its derivatives were shown to have a strong direct antibacterial capacity against four differentserotype 2 strains (P1/7, S735, D282, and OV625) in bacterial medium and even stronger in cell culture medium. In addition, d-CATH-2 and its derivatives ameliorated the efficiency of mouse bone marrow-derived macrophages (BMDM) and skewed mouse bone marrow-derived dendritic cells (BMDC) towards cells with a more macrophage-like phenotype. The peptides directly bind lipoteichoic acid (LTA) and inhibit LTA-induced activation of macrophages. In addition,killed by the peptide was unable to further activate mouse macrophages, which indicates thatwas eliminated by the previously reported silent killing mechanism. Administration of d-C(1-21) at 24 h or 7 days before infection resulted in a small prophylactic protection with reduced disease severity and reduced mortality of the treated mice. CONCLUSION: d-enantiomers of CATH-2 show promise as anti-infectives against pathogenicfor application in mammals.