Hase T, Summers P L, Cohen W H
Department of Ultrastructural Pathology, Walter Reed Army Institute of Research, Washington, D.C.
Arch Virol. 1989;108(1-2):101-14. doi: 10.1007/BF01313747.
The entry modes of Semliki Forest virus and Japanese encephalitis virus into C6/36 cells were compared by electron microscopic observation. At physiological pH, the two viruses showed characteristically different entry modes. Following attachment to the plasma membrane, many SF virions appeared within plasma membrane invaginations and cytoplasmic vesicles; on the other hand, JE virions remained to be found exclusively at the cell surface, with no virions appearing within cytoplasmic vesicles. Electron microscopic observation, therefore, indicated that SF virus entered C6/36 cells by receptor-mediated endocytosis, while JE virus penetrated the cells at the surface and disintegrated at or near the adsorption sites. At pH 5.8, SF virus also entered C6/36 cells by direct penetration at the cell surface. On the basis of the present and other findings, the following working hypotheses are presented for future investigations: (a) at physiological pH, the fusion protein of SF virus is in an inactive state and needs to be activated by acidic pH within the endosome in order to act on the host-cell membrane, but that of JE virus is in an active state and is capable of dissolving the host plasma membrane at the cell surface immediately after the attachment; (b) the states of viral fusion proteins (inactive or active) at the time of viral attachment to the cell surface determine which of the two entry modes these viruses follow.
通过电子显微镜观察比较了塞姆利基森林病毒和日本脑炎病毒进入C6/36细胞的方式。在生理pH值下，这两种病毒表现出明显不同的进入方式。在附着于质膜后，许多SF病毒粒子出现在质膜内陷和细胞质小泡中；另一方面，JE病毒粒子仅在细胞表面被发现，细胞质小泡内未出现病毒粒子。因此，电子显微镜观察表明，SF病毒通过受体介导的内吞作用进入C6/36细胞，而JE病毒在细胞表面穿透细胞并在吸附位点或其附近解体。在pH 5.8时，SF病毒也通过在细胞表面直接穿透进入C6/36细胞。基于目前及其他研究结果，提出以下工作假设以供未来研究：(a)在生理pH值下，SF病毒的融合蛋白处于无活性状态，需要在内体中的酸性pH值下被激活才能作用于宿主细胞膜，而JE病毒融合蛋白处于活性状态，在附着后能立即在细胞表面溶解宿主质膜；(b)病毒附着于细胞表面时病毒融合蛋白的状态（无活性或有活性）决定了这些病毒采用两种进入方式中的哪一种。
