昆虫天然免疫反应分子机制研究进展

Progress in the molecular mechanisms of the innate immune responses in insects

昆虫体内缺乏高等脊椎动物所具有的获得性免疫系统,只能依赖发达的天然免疫系统抵抗细菌、真菌、病毒等外源病原物的侵染。本文概括了昆虫天然免疫反应发生和作用的分子机制相关进展,重点阐述了重要免疫相关因子在昆虫天然免疫反应中的功能和作用机制。昆虫天然免疫反应分为体液免疫和细胞免疫两种,二者共同作用完成对病原物的吞噬(phagocytosis)、集结(nodulation)、包囊(encapsulation)、凝结(coagulation)和黑化(melanization)等。当昆虫受到外界病原物的侵染时,首先通过体内的模式识别蛋白(pattern recognition proteins/receptor,PRPs)识别并结合病原物表面特有的模式分子(pathogen-associated molecular pattern,PAMPs),继而一系列包括丝氨酸蛋白酶和丝氨酸蛋白酶抑制剂在内的级联激活反应被激活和调控,产生抗菌肽、黑色素等免疫效应分子,清除或杀灭外源物。抗菌肽是一类小分子量的阳离子肽,具有广谱抗菌活性,针对不同类型的病原物,抗菌肽的产生机制也不尽相同。昆虫体内存在着两种信号转导途径调节抗菌肽的产生:一是由真菌和大部分革兰氏阳性菌激活的Toll途径;二是由革兰氏阴性菌激活的Imd途径(immune deficiency pathway)。这两个途径通过激活不同转录因子调控不同抗菌肽基因的表达参与昆虫体内的天然免疫反应。

Insects lack acquired immune system processed by vertebrates, and rely solely on developed innate immune system to defend against the infection from alien pathogens such as bacteria, fungi, or virus and so on. In this article, we review the progress in the molecular mechanisms of the development and action of the innate immune responses in insects, especially focusing on the roles and functioning mechanisms of some important immune-related molecules. The innate immune response in insects is divided into humoral immunity and cellular immunity. They function together to kill and eliminate the pathogens via phagocytosis, nodulation, encapsulation, coagulation, and melanization. When the insects are infected by the alien pathogens, the pattern recognition proteins/receptor （PRPs） in insects would firstly recognize and combine with pathogen-associated molecular pattern （PAMPs） in the pathogens, and then initiate the activation and regulation of a series of innate immune response containing immune-related serine proteases and serine protease inhibitors, and finally trigger the production of the immune effectors, such as antimicrobial peptides, melanin and so on, to kill the alien pathogens. The antimicrobial peptides are a kind of cationic peptides with low molecular weight, and have a broad spectrum of antimicrobial activity. They are produced via various mechanisms based on the types of invading pathogens. There are two signal transduction pathways regulating the production of antimicrobial peptides： Toll pathway activated by fungi and most of gram-positive bacteria, and Imd pathway initiated by gram-negative bacteria. These two pathways are contributed to the expression of different antimicrobial peptides due to the activation of different transcription factors.