Molecular Mechanisms to Attenuate Leishmania Parasite

摘要：利什曼原虫引起人类疾病，其临床症状从自愈的皮肤病变到致命的内脏感染。此外，在流行地区，感染艾滋病毒的人特别容易感染利什曼原虫，潜伏感染可在感染艾滋病毒后重新激活。由于缺乏对这种寄生虫的细胞生物学和致病机制的了解，控制这种严重的全球健康风险的任务变得困难。在美国本土，美国军事人员、他们的家人以及访问或居住在疫情地区的其他旅行者尤其感到担忧。为了寻找新的方法来控制这种病原体，我们已经开始研究寄生虫从无毒（promastigote）到有毒（amastigote）的分化机制。利什曼原虫的膜或分泌蛋白与其防御宿主杀死的机制有关。对于利什曼原虫的糖基化/折叠以及膜和分泌蛋白的细胞内转运的重要性，我们知之甚少。已知内质网常驻伴侣蛋白在这些过程中起重要作用。进一步，我们认为分泌过程的改变可能导致利什曼原虫毒力的衰减。我们从多诺瓦利什曼原虫中克隆了钙网蛋白和蛋白二硫异构酶（PDI）等伴侣蛋白的同源物。利什曼原虫中钙网蛋白或PDI显性阴性形式的表达影响了一种必需分泌蛋白——s-酸性磷酸酶（sAcP）的分泌。这些寄生虫被证明更容易被巨噬细胞杀死。这些研究表明，改变利什曼推定的毒力因子的分泌可导致其传染性的衰减。

Summary: The Leishmania parasite causes human disease with clinical symptoms ranging from-self healing cutaneous lesions to a fatal visceral infection. Additionally, in endemic areas, people infected with HIV are especially prone to Leishmania infection and latent infections can reactivate upon acquisition of HIV. The lack of understanding of cell biology and pathogenic mechanisms of this parasite makes the task of controlling this grave, worldwide health risk difficult. Closer to home, it is particularly of concern to U.S. military personnel, their families and other travellers visiting or living in the endemic areas. To find novel methods for control of this pathogen, we have initiated study to understand the mechanism of parasite differentiation from the avirulent (promastigote) to virulent (amastigote) form. Membrane or secretory proteins of Leishmania have been implicated for its defense mechanism against killing by the host. Very little is known about the importance of gylcosyation/folding and intracellular transport of membrane and secretory proteins in Leishmania. ER resident chaperone proteins are known to play an essential role in these processes. Further we argued that alteration of the secretion process might result in attenuation of virulence in Leishmania. We have cloned several homologues of such chaperone proteins such as calreticulin and protein disulfide isomerase (PDI) from Leishmania donovani. Expression of dominant negative forms of calreticulin or PDI in Leishmania affected the secretion of one of the essential secretory proteins, s-acid phosphatase (sAcP). Such parasites were shown to be more prone to killing by the macrophages. These studies suggest that alteration in the secretion of Leishmanial putative virulent factors can result in the attenuation of its infectivity.