The requirement of environmental acidification for Ibaraki virus infection to host cells

TSURUTA, Yuya; SHIBUTANI, Shusaku T.; WATANABE, Rie; IWATA, Hiroyuki

Results obtained in this approach confirmed the usage of clathrin-dependent endocytosis pathway by orbivirus and support the previous report [8] . In addition, it was proved that the exposure to low pH environment is the essential condition to initiate IBAV infection. In the presence of Baf A1, the acidification of late endosome, as well as its fusion to lysosome is impaired [20, 21] . Although the cell surface viruses could be internalized during the post-treatment, they cannot be exposed to low pH environment in the presence of Baf A1. However, if viruses were exposed to low pH at the cell surface before internalization, they acquired the infectivity and could start infection under the effect of Baf A1. PBS (pH4) failed to enhance IBAV infection under the influence of other two inhibitors. Since those two inhibitors interrupt endosome pathway at the very beginning, no IBAV could be incorporated during post-treatment. This might make both IBAV groups to start infection at the same time and resulted in the same viral titer. Since we could not deny an involvement of any proteases, additional research will be required to reveal the entire molecular mechanism of orbivirus infection. The importance of low pH environment for IBAV activation that we proved in this study will help to design experimental approach for further studies.