Apoptosis Induced by a Marine Birnavirus in Established Cell Lines from Fish

Abstract

This study was undertaken to determine whether marine birnavirus (MABV) can induce apoptosis in vitro in cell lines established from four different fish species. MABV Y-6 strain was inoculated onto chinook salmon embryo (CHSE-214), red sea bream kidney (RSBK-2), fathead minnow caudal peduncle (FHM) and epithelioma papulosum cyprini (EPC) cell lines at a multiplicity of infection (m.o.i.) of 0.1. At 0, 12, 24, 36, 48, 72, and 96 h post-infection, the cells were harvested and used for DNA fragmentation analysis, apoptotic cell counts and determination of virus titer by plaque assay. MABV infection appeared to induce the typical features of apoptosis such as nuclear and cytoplasmic condensation, DNA fragmentation and formation of apoptotic bodies in CHSE-214 and RSBK-2 cells, but not in FHM and EPC cells. The concentration of free virus increased immediately after infection, whereas the apoptotic cell ratio and cell-associated virus titer scarecely increased until 24 h. Apoptotsis increased after 36 h when monitored by counting of apoptotic cells and analysis of DNA. The results suggest that MABV replicating to high concentrations during an early stage of infection induces apoptosis in later stages.