Complement in basic processes of the cell

Abstract

The complement system is reemerging in the last few years not only as key element of innate immunityagainst pathogens, but also as a main regulator of local adaptive responses, affecting dendritic cells as wellas T and B lymphocytes. We review data showing that leucocytes are capable of significant autocrine syn-thesis of complement proteins, and express a large range of complement receptors, which in turn regulatetheir differentiation and effector functions while cross talking with other innate receptors such as Toll-like receptors. Other unconventional roles of complement proteins are reviewed, including their impactin non-leukocytes and their intracellular cleavage by vesicular proteases, which generate critical cuesrequired for T cell function. Thus, leucocytes are very much aware of complement-derived information,both extracellular and intracellular, to elaborate their responses, offering rich avenues for therapeuticintervention and new hypothesis for conserved major histocompatibility complex complotypes.