Early interactions of marine birnavirus infection in several fish cell lines.

Marine birnavirus (MABV), a member of the genus Aquabirnavirus, family Birnaviridae, is an unenveloped icosahedral virus with two genomes of double-stranded RNA. The mechanisms of MABV adsorption and penetration are still undetermined. This work examined MABV infection in susceptible and resistant fish cell lines. MABV adsorbed not only onto the cell surfaces of susceptible (CHSE-214 and RSBK-2) cells but also onto resistant (FHM and EPC) cells. Furthermore, the virus entered the cytoplasm through the endocytotic pathway in CHSE-214, RSBK-2 and FHM cells but did not penetrate EPC cells. Thus, restriction of the MABV replication cycle is different between resistant FHM and EPC cells. The virus was found to bind to an around 250 kDa protein on CHSE-214, RSBK-2, FHM and EPC cells. Thus, this 250 kDa protein may be a major MABV receptor that exists in the plasma membranes of all four cell lines examined. This result suggests further that another receptor for virus penetration may exist in CHSE-214, RSBK-2 and FHM cells but not in EPC cells.