Endogenous Antimicrobial Peptide Expression in Response to Bacterial Epidermal Colonization

Abstract

Bacterial commensal colonization of human skin is vital for the training and maintenance of the skin's innate and adaptive immune functions. In addition to its physical barrier against pathogen colonization, the skin expresses a variety of antimicrobial peptides (AMPs) which are expressed constitutively and induced in response to pathogenic microbial stimuli. These AMPs are differentially effective against a suite of microbial skin colonizers, including both bacterial and fungal residents of the skin. We review the breadth of microorganism-induced cutaneous AMP expression studies and their complementary findings on the efficacy of skin AMPs against different bacterial and fungal species. We suggest further directions for skin AMP research based on emerging skin microbiome knowledge in an effort to advance our understanding of the nuanced host-microbe balance on human skin. Such advances should enable the scientific community to bridge the gap between descriptive disease-state AMP studies and experimental single-species in vitro studies, thereby enabling research endeavors that more closely mimic the natural skin environs.

Keywords: antimicrobial peptides; cathelicidin; dermatology; human beta defensins; microbial immunology; psoriasin.

Figure 1

Biogeographical distribution of cutaneous antimicrobial peptide’s (AMP’s)—Gross topographical distribution of AMP expression on healthy human skin has been described by Gläser et al. (10), Falconer et al. (57), Wittersheim et al. (58), and Köten et al. (59). (A) hBD1 is secreted at a higher level on the abdomen and chest than elsewhere, whereas higher expression of (B) hBD2 and (C) hBD3 is reported on the cheeks and forehead, respectively. (D) Two studies (10, 58) examining the biogeography of Psoriasin expression reported similar results on the face, yet differences between the two studies can be seen on the palms, arms, chest, abdomen and calves (studies are represented independently on either side of the caricature). (E) Discrepancies between the two reports (58, 59) on RNase 7 biogeography are less dramatic, with both studies reporting higher expression on facial sites, chest, and abdomen than on arms or legs. For all examined AMPs, the variability of expression between body sites is significant, yet the biological factors leading to such expression patterns are not understood.