The pupal ectoparasitoid Pachycrepoideus vindemiae injects venom into its fly hosts prior to oviposition. We have shown that this venom causes immune suppression in Drosophila melanogaster pupa but the mechanism involved remained unclear. Here, we show using transgenic D. melanogaster with fluorescent hemocytes that the in vivo number of plasmatocytes and lamellocytes decreases after envenomation while it has a limited effect on crystal cells. After in vitro incubation with venom, the cytoskeleton of plasmatocytes underwent rearrangement with actin aggregation around the internal vacuoles, which increased with incubation time and venom concentration. The venom also decreased the lamellocytes adhesion capacity and induced nucleus fragmentation. Electron microscopy observation revealed that the shape of the nucleus and mitochondria became irregular after in vivo incubation with venom and confirmed the increased vacuolization with the formation of autophagosomes-like structures. Almost all venom-treated hemocytes became positive for TUNEL assays, indicating massive induced apoptosis. In support, the caspase inhibitor Z-VAD-FMK attenuated the venom-induced morphological changes suggesting an involvement of caspases. Our data indicate that P. vindemiae venom inhibits D. melanogaster host immunity by inducing strong apoptosis in hemocytes. These assays will help identify the individual venom component(s) responsible and the precise mechanism(s)/pathway(s) involved.

中文翻译：

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外寄生蜂 Pachycrepoideus vindemiae（膜翅目：翅蝽科）的毒液诱导果蝇血细胞凋亡。


蛹外寄生蜂Pachycrepoideus vindemiae 在产卵前将毒液注入苍蝇宿主体内。我们已经证明这种毒液会导致果蝇蛹的免疫抑制，但所涉及的机制仍不清楚。在这里，我们使用带有荧光血细胞的转基因黑腹果蝇表明，毒入后体内浆细胞和层状细胞的数量减少，而对晶体细胞的影响有限。与毒液体外孵育后，浆细胞的细胞骨架发生重排，肌动蛋白聚集在内部液泡周围，并随着孵育时间和毒液浓度的增加而增加。毒液还降低了层状细胞的粘附能力并诱导细胞核碎裂。电镜观察显示，与毒液在体内孵育后，细胞核和线粒体的形状变得不规则，并证实空泡化增加，并形成自噬体样结构。几乎所有毒液处理的血细胞在 TUNEL 检测中均呈阳性，表明大量诱导细胞凋亡。作为支持，半胱天冬酶抑制剂 Z-VAD-FMK 减弱了毒液诱导的形态变化，表明半胱天冬酶的参与。我们的数据表明， P. vindemiae毒液通过诱导血细胞强烈凋亡来抑制黑腹果蝇宿主免疫。这些测定将有助于识别负责的各个毒液成分以及所涉及的精确机制/途径。