African horse sickness virus infects BSR cells through macropinocytosis.

Cellular pathways involved in cell entry by African horse sickness virus (AHSV), a member of the Orbivirus genus within the Reoviridae family, have not yet been determined. Here, we show that acidic pH is required for productive infection of BSR cells by AHSV-4, suggesting that the virus is likely internalized by an endocytic pathway. We subsequently analyzed the major endocytic routes using specific inhibitors and determined the consequences for AHSV-4 entry into BSR cells. The results indicated that virus entry is dynamin dependent, but clathrin- and lipid raft/caveolae-mediated endocytic pathways were not used by AHSV-4 to enter and infect BSR cells. Instead, binding of AHSV-4 to BSR cells stimulated uptake of a macropinocytosis-specific cargo and inhibition of Na(+)/H(+) exchangers, actin polymerization and cellular GTPases and kinases involved in macropinocytosis significantly inhibited AHSV-4 infection. Altogether, the data suggest that AHSV-4 infects BSR cells by utilizing macropinocytosis as the primary entry pathway.