The Complement System of Amphioxus

In this chapter we discuss the gene composition and functions of the complement system of amphioxus. Amphioxus contains only one C3 protein but dozens of complement-related serine proteases. The system can be activated by at least two functional lectin pathways, mediated by C1q and ficolin proteins. Amphioxus has several homologs for the C6 protein, but no classical membrane attack complex has been found. In addition, the amphioxus genome encodes dozens of C1q, collectin-like and ficolin-like proteins, and hundreds of CCP-containing genes.