Influenza D virus diverges from its related influenza C virus in the recognition of 9-O-acetylated N-acetyl- or N-glycolyl-neuraminic acid-containing glycan receptors.

Influenza D virus (IDV) utilizes bovines as a primary reservoir with periodical spillover to other mammalian hosts. By using traditional hemagglutination assay coupled with sialoglycan microarray (SGM) platform and functional assays, we demonstrated that IDV is more efficient in recognizing both 9-O-acetylated N-acetylneuraminic acid (Neu5,9Ac2) and 9-O-acetylated N-glycolylneuraminic acid (Neu5Gc9Ac) than influenza C virus (ICV), a ubiquitous human pathogen. ICV seems to strongly prefer Neu5,9Ac2 over Neu5Gc9Ac. Since Neu5Gc9Ac is different from Neu5,9Ac2 only by an additional oxygen in the group at the C5 position, our results reveal that the hydroxyl group in Neu5Gc9Ac plays a critical role in determining receptor binding specificity, which as a result may discriminate IDV from ICV in communicating with 9-O-acetylated SAs. These findings shall provide a framework for further investigation towards better understanding of how newly discovered multiple-species-infecting IDV exploits natural 9-O-acetylated SA variations to expand its host range.