The activation of insects’ immune system due to the ingestion of microplastics (MPs) has only been evidenced by the upregulation of specific genes. The activation of phenoloxidase (PO) system is one of the primary responses involved in insects' innate immunity when facing parasites and pathogens, and ingestion of MPs can trigger a similar process. This study aimed at addressing the activities of basal PO and total PO (PO+ prophenoloxidase – proPO), in Chironomus riparius larvae (a model species in ecotoxicology) exposed to sediments spiked with polyethylene microplastics (PE-MPs; size-range 32–63 µm; concentrations: 1.25; 5; to 20 g kg^–1) for 48 h. The ingestion of PE-MPs by larvae triggered a significant increase of basal PO activity at 5 and 20 g PE-MPs kg^–1, by 26% and 29%, respectively, whereas total PO increased significantly in the latter (+48%), suggesting de novo synthesis of proPO by organisms. Considering the particle size, the immune response's activation is probably linked to damage in the epithelial cells of the gut lumen. This research work provides the first evidence on the activation of the insect's innate immune system after ingestion of MPs and underlines the PO activity as a good indicator of the immune response induced by MPs' ingestion.

摄入微塑料（MPs）引起的昆虫免疫系统激活仅通过特定基因的上调来证明。当面对寄生虫和病原体时，酚氧化酶（PO）系统的激活是昆虫固有免疫力的主要反应之一，而MP的摄入可以触发类似的过程。这项研究的目的是解决暴露于含聚乙烯微塑料（PE-MP；粒径范围为32-63 µm）的沉积物中的Chironomus riparius幼虫（生态毒理学中的模型物种）中基础PO和总PO的活性；浓度：1.25； 5；至20 g kg ^–1），持续48小时。幼虫摄入PE-MPs会在5 g和20 g PE-MPs kg ^–1时显着增加基础PO活性。分别增加了26％和29％，而后者的总PO显着增加（+ 48％），表明生物体从头合成了proPO。考虑到粒径，免疫应答的激活可能与肠腔上皮细胞的损伤有关。这项研究工作为摄取MPs后昆虫固有免疫系统的活化提供了第一个证据，并强调了PO活性是MPs摄取诱导的免疫反应的良好指标。