Matlin K S, Reggio H, Helenius A, Simons K
J Cell Biol. 1981 Dec;91(3 Pt 1):601-13. doi: 10.1083/jcb.91.3.601.
The entry of fowl plague virus, and avian influenza A virus, into Madin-Darby canine kidney (MDCK) cells was examined both biochemically and morphologically. At low multiplicity and 0 degrees C, viruses bound to the cell surface but were not internalized. Binding was not greatly dependent on the pH of the medium and reached an equilibrium level in 60-90 min. Over 90% of the bound viruses were removed by neuraminidase but not by proteases. When cells with prebound virus were warmed to 37 degrees C, part of the virus became resistant to removal b neuraminidase, with a half-time of 10-15 min. After a brief lag period, degraded viral material was released into the medium. The neuraminidase-resistant virus was capable of infecting the cells and probably did so by an intracellular route, since ammonium chloride, a lysosomotropic agent, blocked both the infection and the degradation of viral protein. When the entry process was observed by electron microscopy, viruses were seen bound primarily to microvilli on the cell surface at 0 degrees C and, after warming at 37 degrees C, were endocytosed in coated pits, coated vesicles, and large smooth-surfaced vacuoles. Viruses were also present in smooth-surfaced invaginations and small smooth-surfaced vesicles at both temperatures. At physiological pH, no fusion of the virus with the plasma membrane was observed. When prebound virus was incubated at a pH of 5.5 or below for 1 min at 37 degrees C, fusion was, however, detected by ferritin immunolabeling. t low multiplicity, 90% of the prebound virus became neuraminidase-resistant and was presumably fused after only 30 s at low pH. These experiments suggest that fowl plague virus enters MDCK cells by endocytosis in coated pits and coated vesicles and is transported to the lysosome where the low pH initiates a fusion reaction ultimately resulting in the transfer of the genome into the cytoplasm. The entry pathway of fowl plague virus thus resembles tht earlier described for Semliki Forest virus.
对鸡瘟病毒和甲型禽流感病毒进入犬肾传代细胞（MDCK）的过程进行了生化和形态学研究。在低感染复数和0℃条件下，病毒与细胞表面结合但未被内化。结合过程对培养基的pH值依赖性不大，60 - 90分钟内达到平衡水平。超过90%的结合病毒可被神经氨酸酶去除，但蛋白酶不能。当预先结合病毒的细胞升温至37℃时，部分病毒对神经氨酸酶的去除产生抗性，半衰期为10 - 15分钟。经过短暂的延迟期后，降解的病毒物质释放到培养基中。抗神经氨酸酶的病毒能够感染细胞，可能是通过细胞内途径，因为溶酶体促渗剂氯化铵可阻断感染和病毒蛋白的降解。通过电子显微镜观察进入过程时，在0℃下可见病毒主要结合在细胞表面的微绒毛上，升温至37℃后，被内吞进入有被小窝、有被小泡和大的光滑表面空泡中。在两个温度下，光滑表面内陷和小的光滑表面小泡中也存在病毒。在生理pH值下，未观察到病毒与质膜融合。然而，当预先结合病毒在37℃下于pH 5.5或更低的条件下孵育1分钟时，通过铁蛋白免疫标记检测到了融合。在低感染复数下，90%预先结合的病毒在低pH值下仅30秒后就变成抗神经氨酸酶的，推测发生了融合。这些实验表明，鸡瘟病毒通过有被小窝和有被小泡的内吞作用进入MDCK细胞，并被转运至溶酶体，在那里低pH值引发融合反应，最终导致基因组转移到细胞质中。因此，鸡瘟病毒的进入途径类似于先前描述的Semliki森林病毒的进入途径。
