Mechanisms of recognition of non-self and initiation of defense reactions in insects

本研究项目的最终目的是研究入侵昆虫的细菌、真菌和寄生虫等外来物质被识别为非我的机制，以及非我的识别机制如何与昆虫防御反应的启动相联系。为了达到这一目的，本研究利用家蚕的血淋巴和体壁两种昆虫组织进行了研究，血淋巴中存在酚氧化酶原级联。这种级联反应是由微量的β-1，3-葡聚糖(βG)或肽聚糖(PG)触发的。我们以前已经证明，PG和BetaG分别与肽聚糖识别蛋白(PGRP)和β-1，3-葡聚糖识别蛋白(βGRP)特异性结合时会触发级联反应。虽然推测识别蛋白可能在识别昆虫血腔中的细菌或真菌为非我中起核心作用，但我们对…的化学结构和作用模式的了解更多的识别蛋白质是非常有限的。我们用免疫化学和免疫细胞化学的方法研究了识别蛋白在血腔中的定位，并提出了两种识别蛋白在识别细菌或真菌在血腔中异体识别过程中的作用的工作假说。实验结果表明，在酶原激活过程中，酶原或酶原片段的活性形式对血细胞的吞噬活性和血流动力学活性有调节作用。为了毫不含糊地证明这一可能性，我们目前正在尝试提纯所有ProPO级联组件。我们最近成功地将ProBAEEase及其活性形式纯化到均一状态。预计这种活性酶将被研究是否对血细胞的吞噬或血流动力学活性有影响。昆虫被膜的角质层通常被认为是身体的保护性盔甲和化学惰性(死亡)部分。利用家蚕轴向生长的幼虫，我们可以证明，当角质层磨损部分含有细菌细胞壁成分(脂多糖或肽聚糖)时，角质层向被层的表皮细胞传递信号，指示它们合成抗菌肽(抗菌肽)。抗菌肽被分泌到角质层。磨损角质层上细菌细胞壁组分的存在可引起脂肪体天蚕素mRNA的合成，但在脂肪体和血淋巴中未检测到天蚕素活性。似乎这种没有立即翻译的信息的mRNA合成表明，角质层与细菌细胞壁成分的磨损使整个昆虫身体对细菌感染保持警惕。目前，我们正在研究从含有细菌细胞壁成分的角质层磨损部分发送到表皮细胞和脂肪体的信号的性质。较少

The ultimate end of this research project is to study the mechanism by which foreign materials such as bacteria, fungi and parasites invading insects are recognized as non-self and how the recognition mechanism of non-self is linked to the initiation of defense reactions of insects. To reach the end the present research was carried out using two insect tissues, hemolymph and integument of the silkworm, Bombyx mori.The prophenoloxidase cascade (ProPO cascade) is present in hemolymph. The cascade is triggered by minute amounts of beta-1,3-glucan (beta G) or peptidoglycan (PG). We have shown previously that PG and betaG trigger the cascade when they bind specifically to peptidoglycan recognition protein (PGRP) and beta-1,3-glucan recognition protein (beta GRP), respectively. Although it is speculated that the recognition proteins may play a central role in the recognition of bacteria or fungi as non-self in insect hemocoel, our knowledge of the chemical structures and the mode of action o … More f the recognition proteins is very limited. We investigated the localization of the recognition proteins in hemocoel by immunochemical and immunocytochemical methods and put forward a working hypothesis on the role of the two recognition proteins in the process of recognition of bacteria or fungi as non-self in hemocoel.The components of proPO cascade include more than two serine enzyme zymogens. Experimental results so har obtained suggest that active forms of the zymogens or fragments derived from the zymogens during their activation modulate phagocytotic activity and hemokinetic activity of hemocytes. To prove this possibility unambiguously we are currently trying to purify all proPO cascade components. We recently have succeeded in purifying proBAEEase and its active form to homogeneity. It is expected that the active enzyme will be studied whether it has the effect on the phagocytotic or hemokinetic activity of hemocytes.Cuticle of insect integument is often considered to be a protective armor and chemically inert (dead) part of the body. Using axenically raised larvae of silkworm, Bombyx mori we could demonstrate that the cuticle transmit a signal to epidermal cells of integument to direct them to synthesize antibacterial peptide (cecropin) when the cuticle has bacterial cell wall component (lipopolysaccharide or peptidoglycan) on its abraded part. The antibacterial peptide is secreted to cuticle. The presence of bacterial cell wall component on abraded cuticle was shown to cause the synthesis of cecropin mRNA in fat body, but in this case no cecropin activity was detected in fat body and hemolymph. Seemingly this mRNA synthesis without immediate translation of the message indicate that cuticular abrasion with bacterial cell wall component make the the entire insect body alert to bacterial infection. Currently we are investigating the nature of signal sent to epidermal cells and fat body from the abraded part of cuticle with bacterial cell wall component. Less