Center for Evolutionary and Theoretical Immunology and Department of Biology, University of New Mexico, Albuquerque, New Mexico, United States of America.
Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Lebanon, New Hampshire, United States of America.
PLoS Pathog. 2020 May 15;16(5):e1008572. doi: 10.1371/journal.ppat.1008572. eCollection 2020 May.
The apicomplexan Toxoplasma gondii induces strong protective immunity dependent upon recognition by Toll-like receptors (TLR)11 and 12 operating in conjunction with MyD88 in the murine host. However, TLR11 and 12 proteins are not present in humans, inspiring us to investigate MyD88-independent pathways of resistance. Using bicistronic IL-12-YFP reporter mice on MyD88+/+ and MyD88-/- genetic backgrounds, we show that CD11c+MHCII+F4/80- dendritic cells, F4/80+ macrophages, and Ly6G+ neutrophils were the dominant cellular sources of IL-12 in both wild type and MyD88 deficient mice after parasite challenge. Parasite dense granule protein GRA24 induces p38 MAPK activation and subsequent IL-12 production in host macrophages. We show that Toxoplasma triggers an early and late p38 MAPK phosphorylation response in MyD88+/+ and MyD88-/- bone marrow-derived macrophages. Using the uracil auxotrophic Type I T. gondii strain cps1-1, we demonstrate that the late response does not require active parasite proliferation, but strictly depends upon GRA24. By i. p. inoculation with cps1-1 and cps1-1:Δgra24, we identified unique subsets of chemokines and cytokines that were up and downregulated by GRA24. Finally, we demonstrate that cps1-1 triggers a strong host-protective GRA24-dependent Th1 response in the absence of MyD88. Our data identify GRA24 as a major mediator of p38 MAPK activation, IL-12 induction and protective immunity that operates independently of the TLR/MyD88 cascade.
刚地弓形虫诱导强烈的保护性免疫，依赖于 Toll 样受体（TLR）11 和 12 在小鼠宿主中与 MyD88 一起识别。然而，TLR11 和 12 蛋白在人类中不存在，这启发我们研究 MyD88 不依赖的抗性途径。使用双顺反子 IL-12-YFP 报告小鼠在 MyD88+/+和 MyD88-/-遗传背景下，我们表明在寄生虫挑战后，CD11c+MHCII+F4/80-树突状细胞、F4/80+巨噬细胞和 Ly6G+中性粒细胞是野生型和 MyD88 缺陷型小鼠中 IL-12 的主要细胞来源。寄生虫致密颗粒蛋白 GRA24 诱导宿主巨噬细胞中 p38 MAPK 激活和随后的 IL-12 产生。我们表明，刚地弓形虫在 MyD88+/+和 MyD88-/-骨髓来源的巨噬细胞中触发早期和晚期 p38 MAPK 磷酸化反应。使用尿嘧啶营养缺陷型 I 型刚地弓形虫菌株 cps1-1，我们证明晚期反应不需要寄生虫的活跃增殖，但严格依赖于 GRA24。通过 i.p.接种 cps1-1 和 cps1-1:Δgra24，我们鉴定了由 GRA24 上调和下调的独特趋化因子和细胞因子亚群。最后，我们证明在没有 MyD88 的情况下，cps1-1 触发了强烈的宿主保护性 GRA24 依赖的 Th1 反应。我们的数据确定 GRA24 是 p38 MAPK 激活、IL-12 诱导和保护性免疫的主要介质，该过程独立于 TLR/MyD88 级联。
