Endo Yuichi, Takahashi Momoe, Fujita Teizo
Department of Immunology, Fukushima Medical University, Fukushima 960-1295, Japan.
Immunobiology. 2006;211(4):283-93. doi: 10.1016/j.imbio.2006.01.003. Epub 2006 Apr 17.
Living organisms have strong defense mechanisms against invading microorganisms as survival strategies. One of the defense mechanisms is the complement system, composed of more than 30 serum and cell surface components. This system collaborates in recognition and elimination of pathogens as a part of both the innate and acquired immune systems. The two collagenous lectins, mannose-binding lectin (MBL) and ficolins, are pattern recognition proteins acting in innate immunity and, upon recognition of the pathogens, they trigger the activation of the lectin complement pathway through attached serine proteases (MASPs). A similar lectin-based complement system, consisting of the lectin-protease complex and C3, is present in ascidians, our closest invertebrate relatives and in lamprey, the most primitive vertebrate. Furthermore, a lamprey N-acetylglucosamine (GlcNAc)-binding lectin was identified as the orthlogue of mammalian C1q, and lamprey MASP is suggested as the prototype of MASP-2/C1r/C1s, indicating that the classical complement pathway arose as a part of the innate immune system. Thus, the complement system is one of the most highly organized innate immune systems in invertebrates and jawless vertebrates, and this system has survived in vertebrates with its core components little changed for 600-700 million years.
作为生存策略，生物体对入侵微生物具有强大的防御机制。其中一种防御机制是补体系统，它由30多种血清和细胞表面成分组成。该系统作为固有免疫系统和获得性免疫系统的一部分，协同参与病原体的识别和清除。两种胶原凝集素，即甘露糖结合凝集素（MBL）和纤维胶凝蛋白，是参与固有免疫的模式识别蛋白，在识别病原体后，它们通过附着的丝氨酸蛋白酶（MASP）触发凝集素补体途径的激活。在我们最亲近的无脊椎动物亲属海鞘和最原始的脊椎动物七鳃鳗中，存在一种类似的基于凝集素的补体系统，该系统由凝集素 - 蛋白酶复合物和C3组成。此外，一种七鳃鳗N - 乙酰葡糖胺（GlcNAc）结合凝集素被鉴定为哺乳动物C1q的同源物，七鳃鳗MASP被认为是MASP - 2/C1r/C1s的原型，这表明经典补体途径是作为固有免疫系统的一部分出现的。因此，补体系统是无脊椎动物和无颌脊椎动物中组织最完善的固有免疫系统之一，并且该系统在脊椎动物中得以保留，其核心成分在6亿至7亿年间几乎没有变化。
