1. Department of Pediatrics, University of California, San Diego, California 92161, USA
2. Division of Dermatology, University of California, San Diego, California 92161, USA
3. Veterans Affairs San Diego Healthcare System, San Diego, California 92161, USA
4. Division of Neonatology, Massachusetts General Hospital, Boston, Massachusetts 02114, USA

Correspondence to: Richard L. Gallo^1,2,3 Correspondence and requests for materials should be addressed to R.L.G. (e-mail: Email: rgallo@vapop.ucsd.edu).

Abstract

In mammals, several gene families encode peptides with antibacterial activity, such as the -defensins and cathelicidins^{1, 2, 3}. These peptides are expressed on epithelial surfaces and in neutrophils, and have been proposed to provide a first line of defence against infection by acting as 'natural antibiotics'^{4, 5}. The protective effect of antimicrobial peptides is brought into question by observations that several of these peptides are easily inactivated^{6, 7, 8} and have diverse cellular effects that are distinct from antimicrobial activity demonstrated in vitro^{9, 10, 11, 12, 13}. To investigate the function of a specific antimicrobial peptide in a mouse model of cutaneous infection, we applied a combined mammalian and bacterial genetic approach to the cathelicidin antimicrobial gene family¹⁴. The mature human (LL-37)¹⁵ and mouse (CRAMP)¹⁶ peptides are encoded by similar genes (CAMP and Cnlp, respectively), and have similar -helical structures, spectra of antimicrobial activity and tissue distribution. Here we show that cathelicidins are an important native component of innate host defence in mice and provide protection against necrotic skin infection caused by Group A Streptococcus (GAS).