BACKGROUND Cryptosporidium is a genus of apicomplexan parasites, the causative agents of cryptosporidiosis in humans and/or animals. Although most apicomplexans parasitize within the host cell cytosols, Cryptosporidium resides on top of host cells, but it is embraced by a double-layer parasitophorous vacuole membrane derived from host cell. There is an electron-dense band to separate the parasite from host cell cytoplasm, making it as an intracellular but extracytoplasmic parasite. However, little is known on the molecular machinery at the host cell-parasite interface. METHODS Cryptosporidium parvum at various developmental stages were obtained by infecting HCT-8 cells cultured in vitro. Immunofluorescence assay was used to detect CpEF1α with a polyclonal antibody and host cell F-actin with rhodamine-phalloidin. Recombinant CpEF1α protein was used to evaluate its effect on the invasion by the parasite. RESULTS We discovered that a C parvum translation elongation factor 1α (CpEF1α) was discharged from the invading sporozoites into host cells, forming a crescent-shaped patch that fully resembles the electron-dense band. At the same time, host cell F-actin aggregated to form a globular-shaped plug beneath the CpEF1α patch. The CpEF1α patch remained for most of the time but became weakened and dissolved upon the completion of the invasion process. In addition, recombinant CpEF1α protein could effectively interfere the invasion of sporozoites into host cells. CONCLUSIONS CpEF1α plays a role in the parasite invasion by participating in the formation of electron-dense band at the base of the parasite infection site.

中文翻译：

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微小隐孢子虫延伸因子1α参与了入侵过程中感染部位基本结构的形成。

背景技术隐孢子虫是apicomplexan寄生虫的属，其是人和/或动物中隐孢子虫病的病原体。尽管大多数apicomplexans寄生在宿主细胞的胞质溶胶中，但隐孢子虫仍驻留在宿主细胞的顶部，但是它被来自宿主细胞的双层寄生虫液泡膜所包围。有一条电子致密带将寄生虫与宿主细胞的细胞质分开，使其成为细胞内但胞质外的寄生虫。然而，对于宿主细胞-寄生虫界面的分子机制了解甚少。方法通过感染体外培养的HCT-8细胞获得不同发育阶段的小隐孢子虫。免疫荧光法用于检测多克隆抗体的CpEF1α，以及若丹明-鬼笔环肽的宿主细胞F-肌动蛋白。重组CpEF1α蛋白被用来评估其对寄生虫侵袭的影响。结果我们发现，一个C小病毒翻译延伸因子1α（CpEF1α）从入侵的子孢子中释放到宿主细胞中，形成一个新月形的补丁，完全类似于电子致密带。同时，宿主细胞F-肌动蛋白聚集形成CpEF1α斑块下方的球形塞子。CpEF1α贴片大部分时间都保留着，但在入侵过程完成后变得弱化并溶解。另外，重组CpEF1α蛋白可以有效地干扰子孢子侵入宿主细胞。结论CpEF1α通过参与寄生虫感染位点的电子致密带的形成而在寄生虫入侵中起作用。