Evolution of the complement system.

Abstract

The mammalian complement system constitutes a highly sophisticated body defense machinery comprising more than 30 components. Research into the evolutionary origin of the complement system has identified a primitive version composed of the central component C3 and two activation proteases Bf and MASP in cnidaria. This suggests that the complement system was established in the common ancestor of eumetazoa more than 500 million years ago. The original activation mechanism of the original complement system is believed to be close to the mammalian lectin and alternative activation pathways, and its main role seems to be opsonization and induction of inflammation. This primitive complement system has been retained by most deuterostomes without major change until the appearance of jawed vertebrates. At this stage, duplication of the C3, Bf and MASP genes as well as recruitment of membrane attack components added the classical and lytic pathways to the primitive complement system, converting it to the modern complement system. In contrast, the complement system was lost multiple times independently in the protostome lineage.