鱼类的皮肤是鱼类的一道物理和化学屏障,皮肤粘液除了包围入侵的微生物外,还含有许多抗菌物质,包括抗菌肽、溶菌酶、凝集素和蛋白酶。鱼类的胃肠消化道含有的酸、胆盐和酶类能使病毒和细菌灭活并消化之。多数情况下,皮肤就足以抵抗致病性微生物,而当皮肤受到机械损伤时,这些病原生物就能致病。当微生物进入鱼体组织后,会遇到一系列的可溶性的细胞成分的防御。血浆里的补体系统在识别细菌的过程中起核心作用。其激活产物能裂解细菌,激发炎症,引起吞噬细胞的浸润,提高其吞噬活力。补体能被细菌的组分或其代谢产物直接激活,也可以被C-反应蛋白,凝集素等能直接结合细菌表面的物质间接激活。血浆也含有许多能抑制细菌生长的物质(例如转铁蛋白,抗蛋白酶)或杀菌物质(例如溶菌酶)。鱼类感染病毒后,感染的细胞产生干扰素,引起相邻的细胞的抗病毒机制以免受感染。抗病毒的细胞毒性细胞能裂解病毒感染细胞,降低病毒在其中增殖的速率。因此,先天性防御可以提供一种预先存在的,快速反应的保护力,该系统是非特异性的;与反应缓慢的、温度依赖性的特异性免疫相比,具有很多优势。 Fish’s skin is a physical and chemical barrier to fish. In addition to surrounding invading microorganisms, mucilage contains many antimicrobial substances including antimicrobial peptides, lysozyme, lectins and proteases. Fish’s gastrointestinal digestive tract contains acids, bile salts and enzymes that inactivate and digest viruses and bacteria. In most cases, the skin is sufficient to resist pathogenic microorganisms, which can become pathogenic when the skin is mechanically damaged. When the microorganisms enter the fish tissue, they encounter a series of defenses against soluble cellular components. The complement system in plasma plays a central role in the identification of bacteria. Its activation products can lyse bacteria, stimulate inflammation, cause the infiltration of phagocytes and improve their phagocytic activity. Complement can be bacterial components or metabolites directly activated, but also by C-reactive protein, lectin and other substances that can directly bind to the bacterial surface activation. Plasma also contains many substances that inhibit the growth of bacteria (such as transferrin, anti-protease) or bactericidal substances (such as lysozyme). After the fish is infected with the virus, the infected cells produce interferons, causing the antiviral mechanisms of neighboring cells to be protected from infection. Antiviral cytotoxic cells can lyse the virus-infected cells and reduce the rate at which the virus proliferates. Thus, innate defenses can provide a pre-existing, rapid-response protective force that is non-specific and has many advantages over slow, temperature-dependent specific immunizations.