Host antimicrobial proteins as endogenous immunomodulators.

Host defense mechanisms are multilayered and involve physical as well as chemical barriers, antimicrobial factors as well as a broad set of immunocompetent cells. The mode of action of antimicrobial factors is variable, ranging from opsonisation and agglutination to direct killing of pathogens. In the last years it has become increasingly clear that some of these factors act as endogenous ligands that bind to distinct host receptors, as for example pathogen recognition receptors (PRRs), thereby influencing distinct immunological processes like chemotaxis, modulation of phagocytosis, dendritic cell maturation or the production of cytokines. By that way, these factors are implicated to protect the host by preventing and clearing of microbial infections.