Abstract

Insects have innate immunity comprising cellular and humoral defense reactions. Nodulation is a predominant cellular immune response to bacterial infections and the prophenoloxidase (PPO)-activating system acts in nodulation with a melanization reaction that darkens the nodules and produces reactive oxygen species that probably kill the bacteria. Although several eicosanoid actions have been reported in insect immune functions, these actions are relatively understudied among dipterans. We addressed this gap by exploring nodulation reactions to bacterial infections in the 3^rd instar of the flesh fly Thomsonea argyrostoma. The Gram-positive bacterium, Micrococcus luteus, was injected either alone or coupled with eicosanoids biosynthesis inhibitors (EBIs). Nodulation exhibits a maximum at 24 h post injection. At zero time of control larvae, a constitutive level of phenoloxidase (PO) was found in plasma. Intrahemocoelic injection of M. luteus induces biosynthesis of PPO in hemocytes, and also its release into and activation in plasma via M. luteus challenge. EBIs suppress nodulation and PPO content of both hemocytes and plasma, but not PO content of plasma. The results imply the mediation of eicosanoids in PPO biosynthesis in hemocytes and its release, but not its activation in plasma. The injection of biogenic monoamines Octopamine (OA) and 5-hydroxytryptamine (5-HT) elevates nodulation and PPO biosynthesis and its activation in plasma.

中文翻译：

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类二十烷酸和生物单胺调节肉蝇的结瘤过程和酚氧化酶活性

摘要

昆虫具有包括细胞和体液防御反应的先天免疫。结节是对细菌感染的主要细胞免疫反应，原酚氧化酶 (PPO) 激活系统在结节中发挥作用，通过黑化反应使结节变暗并产生可能杀死细菌的活性氧。尽管已报道了类花生酸在昆虫免疫功能中的几种作用，但这些作用在双翅目动物中的研究相对较少。我们通过探索肉蝇Thomsonea argyrostoma 3^龄细菌感染的结瘤反应来解决这一空白。革兰氏阳性细菌藤黄微球菌单独注射或与类二十烷酸生物合成抑制剂 (EBI) 联合注射。结瘤在注射后 24 小时达到最大。在对照幼虫的零时间，在血浆中发现了酚氧化酶（PO）的组成水平。血腔内注射藤黄微球菌诱导血细胞中 PPO 的生物合成，并通过藤黄微球菌激发将其释放到血浆中并在血浆中激活。EBI 抑制结节和血细胞和血浆中的 PPO 含量，但不抑制血浆中的 PO 含量。结果表明类二十烷酸介导血细胞中 PPO 生物合成及其释放，但不介导其在血浆中的激活。注射生物单胺章鱼胺 (OA) 和 5-羟色胺 (5-HT) 可提高结瘤和 PPO 生物合成及其在血浆中的活化。