Evolution of Complement as an Effector System in Innate and Adaptive Immunity

Abstract

For a long time, the complement system in mammals has been regarded as a biological system that plays an essential role in innate immunity. More recently, it has been recognized that the complement system contributes heavily to the generation and development of an acquired immune response. In fact, this ancient mechanism of defense has evolved from a primitive mechanism of innate immune recognition in invertebrate species to that of an effector system that bridges the innate with the adaptive immune response in vertebrate species. When and how did complement evolve into a shared effector system between innate and adaptive immunity? To answer this question, our group is interested in understanding the role of complement in innate and adaptive immune responses in an evolutionary relevant species: the teleost fish. The attractiveness of this species as an animal model is based on two important facts. First, teleost fish are one of the oldest animal species to have developed an adaptive immune response. Second, the complement system of teleost fish offers a unique feature, which is the structural and functional diversity of its main effector protein, C3, the third component of the complement system.

Complement in disease: a defence system turning offensive

“…This ‘bridging’ ability seems to have been conserved throughout evolution; in fish, among the most primitive species with both innate and adaptive immune systems, C3b has a role in the uptake of antigens by APCs, increasing the efficacy of antigen presentation and proliferation of B and T cells 72–74 . As mentioned earlier, iC3b and C3dg bind to CR2 (CD21), which is part of the B cell co-receptor complex (FIG.…”

Alternative complement pathway of channel catfish (Ictalurus punctatus): Molecular characterization, mapping and expression analysis of factors Bf/C2 and Df

“…Based on the sequence information and structure domains, it was hard to determine whether these molecules were bona fide factor B or C2 proteins, so they were described as factor Bf/C2 [12].…”

Cloning, Expression, Cellular Distribution, and Role in Chemotaxis of a C5a Receptor in Rainbow Trout: The First Identification of a C5a Receptor in a Nonmammalian Species

“…An additional C3 protein (C3-2) has been reported in rainbow trout that apparently lacks hemolytic activity (45). Trout C4 has recently been cloned, purified, and functionally characterized in our laboratory (46). In addition, a C5 trout molecule has been purified (47) and partially cloned (48).…”