**Cathelicidin, LL-37, hCAP18**

Cathelicidin is found in eccrine gland cells, but also released into circulation. The CAP18 precursor is produced in skin by keratinocytes and is processed within neutrophils, keratinocytes and mast cells by inflammation or injury. In circulation, the mature form is LL-37, after processing of CAP18 by neutrophil-derived elastase and proteinase-3, but other proteases can also produce KS-30 and RK-21, two peptides active against pathogenic bacteria. Cathelicidin expression is also regulated at the transcriptional level by bacterial LPS, cutaneous injury and pro-inflammatory mediators (IL-6, retinoic acid). The LL-37 is intensively studied and besides its wide antibacterial spectrum, it is considered as a mediator between innate and adaptive immunity (Kai-Larsen & Agerberth, 2008) and cell differentiation can also regulate its activity.
