The antimicrobial peptide LL-37: Friend or foe?

Antimicrobial peptides (AMPs) provide broad spectrum antimicrobial defense in both healthy and injured skin. The human cathelicidin antimicrobial peptide LL-37 is involved in various aspects of skin biology, including protection against infection, wound healing, and also in psoriasis. At high concentrations AMPs can damage normal human cells, resulting in necrosis or apoptotic death. Apoptosis is critical in tissue repair and its deregulation seems vital in psoriasis. Despite being involved in cell death of several cell types, virtually nothing is known about the function of LL-37 in keratinocyte apoptosis. Recently Chammorro et al. showed that LL-37 inhibits caspase-3 involving COX-2 and induction of prostaglandin E-2. This explains how the keratinocyte, which secretes AMPs, can remain immune to selfinflicted AMP-induced apoptosis. Thus, overexpression of LL-37 may contribute to reduced keratinocyte apoptosis in conditions such as psoriasis and skin-cancer. Making use of this newly found anti-apoptotic ability could provide new therapeutic options in divers (skin) diseases with lowgrade apoptosis like psoriasis and skin-cancer.