Mechanisms and Treatment of Chronic, Latent Human Strongyloidiasis

描述(申请人提供)：肠道寄生线虫斯特氏线虫感染全世界约1亿人，在美国贫困社区估计有10万人感染。在其简单的形式下，人类弓形虫病会导致慢性肠炎、腹泻和儿童无法茁壮成长，这是其他土壤传播线虫感染的常见症状。与其他寄生线虫不同的是，腐烂链球菌能够自我感染，因此能够在单个宿主中自我复制。自体感染可能发生在调节良好的低水平，并引起慢性潜伏感染，显然可以持续宿主的一生。在接受免疫抑制化疗或感染HTLV-1的患者中，这些极端的慢性感染可能会进展到自身感染被失调的状态，导致潜在的致命播散性高度感染。类固醇免疫抑制剂的使用经常与高感染性弓形虫病的发作有关，并可在动物模型中刺激类固醇链球菌的自身感染。在探索阶段，该项目将研究类固醇调节类固醇自身感染的机制。我们将测试关于这一监管如何发生的三个非互斥假设。前两个假设是相关的，认为药物类固醇或它们的宿主代谢物分别通过SS-DAF-12核激素受体直接作用于寄生虫，刺激和维持自身感染。这两个假设将在该项目R21阶段的目标1下进行测试，方法是在基于细胞的报告试验中确定常见的药物类固醇，如强的松龙或其常见代谢物是否可以激活SS-DAF-12信号。体内实验将确定，当这些寄生虫被接种到宿主中时，用药物类固醇对幼虫进行预处理是否会增强这些寄生虫的自身感染。类固醇调节自身感染的第三个假设是，这是通过抑制宿主的免疫系统，从而使其对这一过程更具容许性，以间接方式发生在寄生虫身上的。我们将在R21阶段的目标2下测试这一假设，方法是去除保留在先天性免疫缺陷NSG小鼠中的免疫效应细胞群，并确定自身感染是否独立于类固醇治疗而发生。达到包括类固醇对S-stercoris的直接影响的证据的里程碑将支持该项目进展到翻译R33阶段，在该阶段，在目标3下，来自用于高通量筛选SS-DAF-12激动剂和拮抗剂的小分子文库的现有系统中的命中化合物将优先用于体内测试。在R33阶段的目标4下，HITS将在模拟药物诱导的自身感染的沙土鼠模型中测试预防自身感染的有效性，如果R21阶段的结果允许，将在由潜在免疫缺陷刺激的自发自身感染的NSG小鼠模型中测试HITS的有效性。标志着R33阶段成功的里程碑将是三种先导化合物，它们清除了超慢性斯特拉菌感染。

DESCRIPTION (provided by applicant): The intestinal parasitic nematode Strongyloides stercoralis infects approximately 100 million people worldwide and an estimated 100,000 in impoverished communities in the USA. In its uncomplicated form, human strongyloidiasis results in chronic enteritis, diarrhea and failure to thrive in children, a syndrome common to other soil-transmitted nematode infections. Unlike other parasitic nematodes, S. stercoralis is capable of autoinfection, and therefore self-replication in individual hosts. Autoinfection may occur at a low well-regulated level and give rise to chronic, latent infections that can apparently last for the lfe of the host. In patients subjected to immunosuppressive chemotherapy or infected by HTLV-1, these exceedingly chronic infections may progress to states in which autoinfection is dysregulated, resulting in potentially fatal disseminated hyperinfection. Use of steroidal immunosuppressants is frequently associated with episodes of hyperinfective strongyloidiasis, and can stimulate autoinfection by S. stercoralis in animal models. In its exploratory phase, this project will examine the mechanism by which steroids regulate autoinfection by S. stercoralis. We will test three non-mutually exclusive hypotheses of how this regulation occurs. The first two hypotheses are related and hold that medicinal steroids or their host metabolites, respectively, act directly on the parasite via its Ss-DAF-12 nuclear hormone receptor to stimulate and maintain autoinfection. These two hypotheses will be tested under Aim 1 of the R21 phase of the project by ascertaining whether common medicinal steroids such as prednisolone or its common metabolites can activate Ss-DAF-12 signaling in a cell based reporter assay. In vivo experiments will ascertain whether pre-treatment of larval S. stercoralis with medicinal steroids can potentiate autoinfection when these parasites are inoculated into a host. The third hypothesis of steroid regulation of autoinfection is that this occurs in an indirect manner with respect to the parasite by suppressing the host's immune system and thereby rendering it more permissive for this process. We will test this hypothesis under Aim 2 of the R21 phase by ablating immune effector cell populations that remain in the congenitally immune-deficient NSG mouse and ascertaining whether autoinfection occurs independent of steroid treatment. Attainment of milestones comprising evidence of direct steroid effects on S. stercoralis will support progression of the project to a translational R33 phase where, under Aim 3, compounds arising as hits from an existing system for high-throughput screening of small-molecule libraries for agonists and antagonists of Ss-DAF-12 will be prioritized for in vivo testing. Under Aim 4 in the R33 phase, hits will be tested for efficacy in preventing autoinfection in a gerbil model simulating drug-induced autoinfection, and, if results from the R21 phase allow, in an NSG mouse model of spontaneous autoinfection stimulated by underlying immune deficiency. Milestones indicating success in the R33 phase will be three lead compounds that clear hyperchronic S. stercoralis infection.