Human antimicrobial peptides

Antimicrobial peptides are ancient in origin but are thought to play an imp ortant integral role in human innate immunity. In recent years, there has b een an increased understanding of the diversity of animal antimicrobial pep tides in general and human antimicrobial peptides in particular. Currently, five families of antimicrobial peptides have been described in humans. The se are the alpha-defensins with six members, the beta-defensins with two me mbers, a single cathelicidin, LL-37, the histatin family with three main me mbers and the recently described two thrombin-induced platelet antimicrobia l peptides (the thrombocidins). With the exception of LL-37, families of an timicrobial peptides are associated with specific tissues. A number of anti microbial peptides may be generated in vitro by non-specific proteolysis of extracellular proteins. Two of these, the acidic antimicrobial peptides an d lactoferricin derived by pepsin digestion of lactoferrin may have roles i n vivo. Recent work has demonstrated that the expressions of several peptid es are upregulated by inflammation, beta-defensin 2 and LL-37. There is als o a growing appreciation of the synergistic activity that may be found both between some peptide families and other antimicrobial proteins of the inna te immune system. (C) 2001 Lippincott Williams & Wilkins.