Philadelphia Research and Education Foundation, Philadelphia, Pennsylvania, United States of America.
PLoS Negl Trop Dis. 2013 May 9;7(5):e2224. doi: 10.1371/journal.pntd.0002224. Print 2013.
Infection with the intracellular protozoan parasite Leishmania mexicana causes chronic disease in C57BL/6 mice, in which cutaneous lesions persist for many months with high parasite burdens (10(7)-10(8) parasites). This chronic disease process requires host IL-10 and FcγRIII. When Leishmania amastigotes are released from cells, surface-bound IgG can induce IL-10 and suppress IL-12 production from macrophages. These changes decrease IFN-γ from T cells and nitric oxide production in infected cells, which are both required for Leishmania control. However, antibodies targets and the kinetics of antibody production are unknown. Several groups have been unsuccessful in identifying amastigote surface proteins that bind IgG. We now show that glycoinositol phospholipids (GIPLs) of L. mexicana are recognized by mouse IgG1 by 6 weeks of infection, with a rapid increase between 12 and 16 weeks, consistent with the timing of chronic disease in C57BL/6 mice vs. healing in FcγRIII-deficient mice. A single prominent spot on TLC is recognized by IgG, and the glycolipid is a glycosyl phosphatidylinositol containing a branched mannose structure. We show that the lipid structure of the GIPL (the sn-2 fatty acid) is required for antibody recognition. This GIPL is abundant in L. mexicana amastigotes, rare in stationary-phase promastigotes, and absent in L. major, consistent with a role for antibodies to GIPLs in chronic disease. A mouse monoclonal anti-GIPL IgG recognizes GIPLs on the parasite surface, and induces IL-10 from macrophages. The current work also extends this mouse analysis to humans, finding that L. mexicana-infected humans with localized and diffuse cutaneous leishmaniasis have antibodies that recognize GIPLs, can bind to the surface of amastigotes, and can induce IL-10 from human monocytes. Further characterization of the target glycolipids will have important implications for drug and vaccine development and will elucidate the poorly understood role of glycolipids in the immunology of infections.
感染细胞内原生动物寄生虫利什曼原虫会导致 C57BL/6 小鼠发生慢性疾病，在此过程中，皮肤损伤会持续数月，且寄生虫负荷量很高（10(7)-10(8) 寄生虫）。这种慢性疾病过程需要宿主的白细胞介素 10（IL-10）和 FcγRIII。当利什曼原虫的无鞭毛体从细胞中释放出来时，表面结合的 IgG 可以诱导白细胞介素 10（IL-10）并抑制巨噬细胞产生白细胞介素 12（IL-12）。这些变化会减少 T 细胞产生的 IFN-γ 和感染细胞中的一氧化氮产生，而这两者都是控制利什曼原虫所必需的。然而，抗体的靶点和抗体产生的动力学尚不清楚。几个研究小组都未能鉴定出与 IgG 结合的无鞭毛体表面蛋白。我们现在表明，墨西哥利什曼原虫的糖基肌醇磷脂（GIPLs）在感染后 6 周被小鼠 IgG1 识别，在 12 至 16 周之间迅速增加，与 C57BL/6 小鼠慢性疾病的时间一致，而与 FcγRIII 缺陷型小鼠的愈合一致。TLC 上的一个单一明显斑点被 IgG 识别，而该糖脂是一种含有分支甘露糖结构的糖基磷脂酰肌醇。我们表明，GIPL 的脂质结构（sn-2 脂肪酸）是抗体识别所必需的。这种 GIPL 在墨西哥利什曼原虫的无鞭毛体中含量丰富，在静止期前鞭毛体中很少，在利什曼原虫中不存在，这与抗体针对 GIPLs 在慢性疾病中的作用一致。一种小鼠单克隆抗 GIPL IgG 识别寄生虫表面的 GIPLs，并诱导巨噬细胞产生白细胞介素 10。目前的工作还将这种小鼠分析扩展到人类，发现患有局限性和弥漫性皮肤利什曼病的感染了墨西哥利什曼原虫的人类具有可以识别 GIPLs 的抗体，可以与无鞭毛体的表面结合，并可以诱导人类单核细胞产生白细胞介素 10。对靶糖脂的进一步表征将对药物和疫苗的开发具有重要意义，并将阐明糖脂在感染免疫中作用的理解不足。
