Comparison of endocytosis pathways of Duck Tembusu virus in BHK-21 and duck embryo fibroblasts

The Duck Tembusu virus (DTMUV) is a zoonotic flavivirus characterized by nonsuppurative encephalitis and decreasing egg production that has adversely affected the poultry industry. While the way of invasion of DTMUV into different host cells, especially primary cells, remains elusive. In the present study, the ultrastructural pathological characteristics showed that DTMUV underwent a typical maturation and replication process: progeny virus particles gathered in rough endoplasmic reticulum (RER) cisternae, reached the cell membrane via Golgi body's endocrine channel, then were released in the infected baby hamster kidney-21 (BHK-21) and duck embryo fibroblast (DEF). Endoplasmic reticulum vesicles in BHK-21 were short rods and densely arranged like honeycombs, whereas vesicles in DEF were round and dispersed. Further study showed that the virus replication peak in mammalian BHK-21 cells was at 48 hpi, whereas in avian DEF cells was at 24 hpi. DTMUV entry into BHK-21 and DEF cells was blocked by clathrin inhibitor, chlorpromazine (CPZ), indicating that the flavivirus DTMUV enters BHK-21 and DEF both via a clathrin-mediated endocytosis (CME) pathway rather than caveola-mediated endocytosis or micropinocytosis. The endocytic difference in DTMUV entry into BHK-21 and DEF cells might provide insight into understanding the underlying virulence difference between passaged cells and cultured cells.