Participation of mammalian defensins and cathelicidins in anti‐microbial immunity: receptors and activities of human defensins and cathelicidin (LL‐37)

Defensins and cathelicidins are the two major families of mammalian anti‐microbial proteins. They contribute to host, innate, anti‐microbial defense by disrupting the integrity of the bacterial cell membrane. However, several members of the mammalian anti‐microbial proteins including defensins and cathelicidins have been shown recently to have chemotactic effects on host cells. Human neutrophil α‐defensins are chemotactic for resting, naïve CD45RA/CD4 T cells, CD8 T cells, and immature dendritic cells. Human β‐defensins are also chemotactic for immature dendritic cells but induce the migration of memory CD45RO/CD4 T cells. In contrast, cathelicidin/LL‐37 is chemotactic for neutrophils, monocytes, and T cells but not for dendritic cells. Thus, these anti‐microbial peptides have distinct, host‐target cell spectra. The chemotactic activities of human β‐defensins and cathelicidin/LL‐37 are mediated by human CC chemokine receptor 6 and formyl peptide receptor‐like 1, respectively. The capacities of defensins and cathelicidins to mobilize various types of phagocytic leukocytes, immature dendritic cells, and lymphocytes, together with their other effects such as stimulating IL‐8 production and mast cell degranulation, provide evidence for their participation in alerting, mobilizing, and amplifying innate and adaptive anti‐microbial immunity of the host.