鱼类补体系统的研究进展

鱼类补体大约由30余种蛋白裂解酶、酶抑制因子和受体构成的，是机体内最为复杂的限制性蛋白溶解系统。在鱼类免疫系统进化中，补体的出现比免疫球蛋白还要早。许多研究表明鱼类补体直接参与机体防御，其生物学活性影响机体抵抗微生物的能力、免疫反应细胞间的通讯联系、免疫复合物的形成和持续时间等。

The complement system in fish

Complement is a humoral factor of innate immunity and plays important roles in immune surveillance and clearance of invading pathogens.This system is directly and immediately activated in an immune-competent host,and the alternative(antibody-independent),Lectin(triggered by mannose-binding lectin) and classical pathways(antibody-dependent) have been described in fish.All three pathways converge to the lytic pathway,leading to opsonization or direct killing of the microorganism.The alternative and lectin pathways are ancient mechanisms present in invertebrates as well as ancient vertebrates.Some of the agents,like zymosan and LPS(lipopolysaccharide),are known activators of the alternative pathway of fish complement.The lectin pathway,which has not been much studied in teleosts,is activated by the binding of mannose on the surface of microorganisms to a complex of mannose-binding lectin(MBL) and MBL-associated serine protease(MASP).Fish complements are comparable to those of mammals but some important differences have been described.Fish serum shows hemolytic activity indistinguishable from that of mammalian complement.In general the complement system of the alternative pathway is more active in fish than in mammals,is not heat labile and therefore difficult to preserve.Fish complement has lower optimum reaction temperature than its mammalian counterpart,and its components,like C3.The complement system is composed of numerous proteins and all pathways generate factor C3,which has been described and isolated from teleost species.Complement C3 is a central molecule in the complement system whose activation is essential for all the important functions performed by this system.Complement proteins in fish,like C3 and B factor,are more polymorphic.Here we describe some characteristics of the complement system of fish.