The new face of anaphylatoxins in immune regulation.

Anaphylatoxins are a group of small peptides (i.e. C3a, C4a and C5a) generated by complement activation and play important roles in innate immunity through the initiation and regulation of inflammatory responses. More recent studies have revealed that, in addition to their traditional roles in inflammation, anaphylatoxins also significantly influence the adaptive immune response. It does so through a number of mechanisms and by targeting various cells. One important mechanism is that anaphylatoxins (C3a, C5a) act on their receptors expressed on innate immune cells such as dendritic cells. This modulates cell activation and their functions in initiating and regulating T cell responses and thus influencing T cell immunity. This review provides an overview of anaphylatoxins in adaptive immune regulation focusing on their roles in modulating dendritic cell and macrophage functions and the importance of local production of complement in this regulation.