The Hemagglutinin of Bat-Associated Influenza Viruses Is Activated by TMPRSS2 for pH-Dependent Entry into Bat but Not Human Cells

Hoffmann, Markus; Krüger, Nadine; Zmora, Pawel; Wrensch, Florian; Herrler, Georg; Pöhlmann, Stefan

The finding that batFLUAV surface proteins can facilitate entry into bat-derived target cells allowed us to investigate which viral and cellular components contribute to the entry process. We first focused on NAL. The expression of this protein, unlike expression of NA, in pseudotype-producing cells did not increase the titers of vectors harboring the corresponding bat-FLUAV-HAL protein. However, this finding does not exclude that NAL, like the NA of FLUAV, acts as a receptor-destroying enzyme. Thus, HEK-293T cells used for pseudotype preparation were not susceptible to HAL-driven entry, most likely because they do not express the appropriate receptor. It thus remains to be analyzed whether batFLUAV-NAL increases release of HAL-bearing vectors and authentic batFLUAV from susceptible bat cell lines. These endeavors might be challenging since transfection of bat cell lines by calcium-phosphate precipitation and liposome-based reagents was inefficient (not shown).