Department of Biology, Emory University, Atlanta, GA 30322, USA.
Proc Natl Acad Sci U S A. 2013 Jun 4;110(23):9427-32. doi: 10.1073/pnas.1222351110. Epub 2013 May 20.
Because parasite virulence factors target host immune responses, identification and functional characterization of these factors can provide insight into poorly understood host immune mechanisms. The fruit fly Drosophila melanogaster is a model system for understanding humoral innate immunity, but Drosophila cellular innate immune responses remain incompletely characterized. Fruit flies are regularly infected by parasitoid wasps in nature and, following infection, flies mount a cellular immune response culminating in the cellular encapsulation of the wasp egg. The mechanistic basis of this response is largely unknown, but wasps use a mixture of virulence proteins derived from the venom gland to suppress cellular encapsulation. To gain insight into the mechanisms underlying wasp virulence and fly cellular immunity, we used a joint transcriptomic/proteomic approach to identify venom genes from Ganaspis sp.1 (G1), a previously uncharacterized Drosophila parasitoid species, and found that G1 venom contains a highly abundant sarco/endoplasmic reticulum calcium ATPase (SERCA) pump. Accordingly, we found that fly immune cells termed plasmatocytes normally undergo a cytoplasmic calcium burst following infection, and that this calcium burst is required for activation of the cellular immune response. We further found that the plasmatocyte calcium burst is suppressed by G1 venom in a SERCA-dependent manner, leading to the failure of plasmatocytes to become activated and migrate toward G1 eggs. Finally, by genetically manipulating plasmatocyte calcium levels, we were able to alter fly immune success against G1 and other parasitoid species. Our characterization of parasitoid wasp venom proteins led us to identify plasmatocyte cytoplasmic calcium bursts as an important aspect of fly cellular immunity.
由于寄生虫的毒力因子针对宿主的免疫反应，因此鉴定和功能分析这些因子可以深入了解了解甚少的宿主免疫机制。黑腹果蝇是体液固有免疫的模型系统，但果蝇细胞固有免疫反应仍未得到充分描述。在自然界中，果蝇经常受到寄生蜂的感染，感染后，果蝇会产生细胞免疫反应，最终导致蜂卵的细胞包裹。该反应的机制基础在很大程度上尚不清楚，但是黄蜂使用源自毒液腺的混合毒力蛋白来抑制细胞包裹。为了深入了解黄蜂毒力和果蝇细胞免疫的机制，我们使用联合转录组/蛋白质组学方法从 Ganaspis sp.1（G1）中鉴定出毒液基因，G1 是一种以前未被描述的果蝇寄生蜂物种，并且发现 G1 毒液含有丰富的肌浆/内质网钙 ATP 酶（SERCA）泵。因此，我们发现免疫细胞称为浆血细胞在感染后通常会经历细胞质钙爆发，并且这种钙爆发是激活细胞免疫反应所必需的。我们进一步发现，G1 毒液以 SERCA 依赖的方式抑制浆血细胞的钙爆发，导致浆血细胞无法被激活并向 G1 卵迁移。最后，通过遗传操纵浆血细胞钙水平，我们能够改变果蝇对 G1 和其他寄生蜂物种的免疫成功率。我们对寄生蜂毒液蛋白的表征使我们确定浆血细胞细胞质钙爆发是果蝇细胞免疫的一个重要方面。
