Pooja Makwana, Pradeep Appukuttan Nair R, Hungund Shambhavi P, Sagar Chandrashekhar, Ponnuvel Kangayam M, Awasthi Arvind K, Trivedy Kanika
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Acta Parasitol. 2017 Dec 20;62(4):717-727. doi: 10.1515/ap-2017-0086.
Parasitization of silkworm, Bombyx mori by invasive larva of dipteran parasitoid Exorista bombycis caused upto 20% revenue loss in sericulture. The parasitism was successful by suppressing host immune system however mechanism of immune suppression induced by E. bombycis is unknown which is unravelled here. The infestation induced cytotoxic symptoms in host hemocytes, such as vacuolated cytoplasm, porous plasma membrane, indented nuclei with condensed chromatin and dilated RER. One of the markers of necrosis is cell permeabilization, which can be measured as released lactate dehydrogenase (LDH). LDH level showed significantly (P<0.01) high release into extracellular medium in vitro after exposure of hemocytes to parasitoid larval tissue protein compared with control revealing membrane permeability and loss of cell integrity. At five minutes after exposure, cytotoxicity was 43% and was increased to 99% at 3h. The cytotoxicity is signalled by increased content of hydrogen peroxide (H2O2) causing lipid peroxidation followed by porosity in plasma membrane. A test for lipid peroxidation by measurement of lipid peroxidation breakdown product, malondialdehyde (MDA) revealed significant increase in peroxidation from one to 24 h post-invasion, with maximum at 12 h (P<0.008). Level of reactive oxygen species measured as H2O2 production increased from 6 to 12 h post-invasion and continued to increase significantly (P<0.03) reaching maximum at 48 h. These observations reveal that dipteran endoparasitoid invasion induced H2O2 production in the hemocytes causing cytotoxicity, lipid peroxidation and membrane porosity that suppressed both humoral- and cell-mediated immune responses of hemocytes in B. mori.
双翅目寄生蜂家蚕追寄蝇的侵入性幼虫寄生于家蚕，给养蚕业造成了高达20%的收入损失。这种寄生通过抑制宿主免疫系统而成功，但家蚕追寄蝇诱导免疫抑制的机制尚不清楚，本文对此进行了揭示。这种侵染在宿主血细胞中诱发了细胞毒性症状，如细胞质空泡化、质膜多孔、细胞核凹陷且染色质凝聚以及粗面内质网扩张。坏死的标志物之一是细胞通透性增加，这可以通过释放的乳酸脱氢酶（LDH）来衡量。与对照相比，血细胞暴露于寄生蜂幼虫组织蛋白后，体外LDH水平显著（P<0.01）高释放到细胞外培养基中，表明膜通透性和细胞完整性丧失。暴露后五分钟，细胞毒性为43%，3小时时增加到99%。细胞毒性由过氧化氢（H2O2）含量增加发出信号，导致脂质过氧化，随后质膜出现孔隙。通过测量脂质过氧化分解产物丙二醛（MDA）进行的脂质过氧化测试显示，入侵后1至24小时过氧化显著增加，在12小时时达到最大值（P<0.008）。以H2O2产生量衡量的活性氧水平在入侵后6至12小时增加，并继续显著增加（P<0.03），在48小时时达到最大值。这些观察结果表明，双翅目内寄生蜂的入侵在血细胞中诱导H2O2产生，导致细胞毒性、脂质过氧化和膜孔隙形成，从而抑制了家蚕血细胞的体液免疫和细胞介导免疫反应。
