Deficiency of p110δ Isoform of the Phosphoinositide 3 Kinase Leads to Enhanced Resistance to <i>Leishmania donovani</i>

Background Visceral leishmaniasis is the most clinically relevant and dangerous form of human leishmaniasis. Most traditional drugs for treatment of leishmaniasis are toxic, possess many adverse reactions and drug resistance is emerging. Therefore, there is urgent need for identification of new therapeutic targets. Recently, we found that mice with an inactivating knock-in mutation in the p110δ isoform of pi3k, (p110δd910a) are hyper resistant to L. major, develop minimal cutaneous lesion and rapidly clear their parasite. Here, we investigated whether pi3k signaling also regulates resistance to L. donovani, one of the causative agents of visceral leishmaniasis. Methodology/Principal Findings WT and p110δD910A mice (on a BALB/c background) were infected with L. donovani. At different time points, parasite burden and granuloma formation were assessed. T and B cell responses in the liver and spleen were determined. In addition, Tregs were expanded in vivo and its impact on resistance was assessed. We found that p110δD910A mice had significantly reduced splenomegaly and hepatomegaly and these organs harbored significantly fewer parasites than those of WT mice. Interestingly, infected p110δD910A mice liver contains fewer and less organized granulomas than their infected WT counterparts. Cells from p110δD910A mice were significantly impaired in their ability to produce cytokines compared to WT mice. The percentage and absolute numbers of Tregs in infected p110δD910A mice were lower than those in WT mice throughout the course of infection. In vivo expansion of Tregs in infected p110δD910A mice abolished their enhanced resistance to L. donovani infection. Conclusions/Significance Our results indicate that the enhanced resistance of p110δD910A mice to L. donovani infection is due to impaired activities of Tregs. They further show that resistance to Leishmania in the absence of p110δ signaling is independent of parasite species, suggesting that targeting the PI3K signaling pathway may be useful for treatment of both visceral and cutaneous leishmaniasis.背景 内脏利什曼病（Visceral leishmaniasis）是临床相关性最强、危害性最高的人类利什曼病分型。当前多数治疗利什曼病的传统药物毒性显著、不良反应繁多，且耐药性问题日益凸显，因此亟需鉴定新型治疗靶点。近期本研究发现，携带磷脂酰肌醇3-激酶（PI3K）p110δ亚型失活敲入突变（p110δD910A）的小鼠对硕大利什曼原虫（L. major）具有极强抗性，仅出现极轻微的皮肤病变，并可快速清除体内寄生虫。本研究旨在探究PI3K信号通路是否同样调控宿主对杜氏利什曼原虫（L. donovani）——内脏利什曼病的主要致病菌之一——的抗性。 研究方法与主要实验结果 将野生型（WT）及p110δD910A小鼠（均为BALB/c背景品系）感染杜氏利什曼原虫。于不同时间点评估小鼠体内的寄生虫负荷与肉芽肿形成情况，并检测肝脏与脾脏中的T、B细胞免疫应答。此外，本研究还通过体内扩增调节性T细胞（Tregs），探究其对宿主抗性的影响。 结果显示，p110δD910A小鼠的脾肿大与肝肿大症状显著减轻，且上述器官内的寄生虫载量显著低于野生型小鼠。值得注意的是，感染后的p110δD910A小鼠肝脏内肉芽肿数量更少、结构更松散，相较于感染后的野生型小鼠差异显著。与野生型小鼠相比，p110δD910A小鼠的细胞因子分泌能力显著受损。在整个感染周期中，感染后的p110δD910A小鼠体内调节性T细胞的占比与绝对计数均低于野生型小鼠。通过体内扩增调节性T细胞可消除p110δD910A小鼠对杜氏利什曼原虫感染的增强抗性。 结论与意义 本研究结果表明，p110δD910A小鼠对杜氏利什曼原虫感染的增强抗性源于调节性T细胞功能受损。同时本研究还发现，在缺乏p110δ信号通路的情况下，宿主对利什曼原虫的抗性不受寄生虫物种的影响，这提示靶向PI3K信号通路或可用于治疗内脏利什曼病与皮肤利什曼病。