LL-37-mediated activation of host receptors is critical for defense against group A streptococcal infection

Abstract

Group A Streptococcus (GAS) causes diverse human diseases, including life-threatening soft-tissue infections. It is accepted that the human antimicrobial peptide LL-37 protects the host by killing GAS. Here, we show that GAS extracellular protease ScpC N-terminally cleaves LL-37 into two fragments of 8 and 29 amino acids, preserving its bactericidal activity. At sub-bactericidal concentrations, the cleavage inhibits LL-37-mediated neutrophil chemotaxis, shortens neutrophil lifespan, and eliminates P2X7 and EGF receptors' activation. Mutations at the LL-37 cleavage site protect the peptide from ScpC-mediated splitting, maintaining all its functions. The mouse LL-37 ortholog CRAMP is neither cleaved by ScpC nor does it activate P2X7 or EGF receptors. Treating wild-type or CRAMP-null mice with sub-bactericidal concentrations of the non-cleavable LL-37 analogs promotes GAS clearance that is abolished by the administration of either P2X7 or EGF receptor antagonists. We demonstrate that LL-37-mediated activation of host receptors is critical for defense against GAS soft-tissue infections.

Keywords: CRAMP; EGFR; GAS; LL-37; P2X7R; group A Streptococcus; host-defense peptides; innate immunity; murine models of human GAS soft-tissue infections; neutrophils.