Blouin E F, Kocan K M
Department of Anatomy, Pathology, and Pharmacology, College of Veterinary Medicine, Oklahoma State University, Stillwater 74078-2007, USA.
J Med Entomol. 1998 Sep;35(5):788-97. doi: 10.1093/jmedent/35.5.788.
Anaplasma marginale Theiler, a tick-borne rickettsial pathogen of cattle, was recently propagated in a continuous tick cell line, IDE8, derived from embryonic Ixodes scapularis Say. Cell monolayers were infected briefly with a high multiplicity of infection to synchronize rickettsial development and allow for description of the invasion, development, and release of A. marginale from the cultured cells. Sequential samples were collected, fixed, and processed for examination with light and electron microscopy. A. marginale entered host cells by an endocytotic process and remained within a vacuolar membrane throughout development. After entry, the dense form of A. marginale transformed into the vegetative or reticulated form that multiplied by binary fission, forming large colonies of rickettsiae. The reticulated form subsequently transformed into the dense form of A. marginale, which was released from cells and survived extracellularly. The dense forms were eventually released from the cultured cells by a process in which the inclusion membrane fused with the host cell membrane. Release of A. marginale was effected without the loss of host cell cytoplasm. In subsequent cell cycles, A. marginale reinfected cultured cells resulting in the development of multiple colonies per cell and eventual host cell destruction. Small vesicles were abundant within the colonies and appeared to form from individual rickettsiae. Development of A. marginale in IDE8 cells was similar to that described in naturally infected Dermacentor spp. ticks. However, destruction of cells by A. marginale as seen in vitro was not observed in naturally infected ticks. An understanding of the developmental cycle of A. marginale in cultured cells may provide insight into rickettsial development in its tick host and provide a basis for studying pathogen-host cell interaction in vitro.
边缘无形体泰勒氏菌是一种通过蜱传播的牛立克次氏体病原体，最近在一种连续的蜱细胞系IDE8中得以繁殖，该细胞系源自肩突硬蜱胚胎。用高感染复数对细胞单层进行短暂感染，以使立克次氏体发育同步，并便于描述边缘无形体从培养细胞中的侵入、发育和释放过程。收集连续样本，进行固定和处理，以便用光学显微镜和电子显微镜检查。边缘无形体通过内吞过程进入宿主细胞，并在整个发育过程中保持在液泡膜内。进入后，边缘无形体的致密形态转变为通过二分裂繁殖的营养或网状形态，形成大量立克次氏体菌落。随后，网状形态转变为边缘无形体的致密形态，其从细胞中释放并在细胞外存活。致密形态最终通过包含膜与宿主细胞膜融合的过程从培养细胞中释放出来。边缘无形体的释放过程中宿主细胞细胞质未丢失。在随后的细胞周期中，边缘无形体再次感染培养细胞，导致每个细胞形成多个菌落并最终破坏宿主细胞。菌落在小泡内大量存在，似乎由单个立克次氏体形成。边缘无形体在IDE8细胞中的发育与自然感染的革蜱属蜱中所描述的相似。然而，在自然感染的蜱中未观察到体外所见的边缘无形体对细胞的破坏。了解边缘无形体在培养细胞中的发育周期可能有助于深入了解其在蜱宿主中的立克次氏体发育，并为体外研究病原体与宿主细胞相互作用提供基础。
