Ancient origins: complement in invertebrates

Abstract

Proteins with obvious similarities to mammalian complement are widely distributed in the animal kingdom.In the vertebrate lineage, deuterostomes like sea urchins and tunicates express proteins that arehomologues of C3, the central component of the vertebrate complement cascade. Their genomes alsoencode molecules resembling factor B from the “alternative” complement activation pathway; andtunicates have collagenous lectins of the type that can activate complement in the absence of antibodies.This suggests that the core components of the complement system evolved before antibodies, which firstappear in jawed fish.

Keywords

• C3
• collectins
• complement
• invertebrate immune systems
• TEP proteins