Spatial localization of avian and human influenza A virus receptors in male and female bovine reproductive tissues.

Highly pathogenic avian influenza virus (HPAIV) of the H5N1 type has recently emerged as a major concern in livestock, with widespread outbreaks now confirmed in U.S. dairy cattle. This raises critical questions about the susceptibility of bovine reproductive tissues to viral entry, replication, and potential transmission. Influenza A viruses (IAV) initiate infection through hemagglutinin (HA) binding to host cell surface sialic acid residues, avian-adapted strains preferentially bind α2,3-linked sialic acids, while human-adapted strains bind α2,6-linked residues. This study aimed to characterize the spatial distribution of α2,6-linked sialic acids (human-like receptors), α2,3-Galβ1-4, and α2,3-Galβ1-3 (avian-like receptors) in male and female bovine reproductive tissues using lectin-based histochemistry. Post-mortem reproductive tissues were collected from bulls (n = 4) and multiparous cows (n = 3) and stained with biotinylated lectins. Human-like receptors were detected in the luminal epithelium of the penile urethra, vas deferens, epididymis, seminiferous tubules, vagina, cervix, uterus, oviduct, and mammary gland. Avian-like receptors were also detected in the penile urethra, epididymis, vagina, cervix, oviduct, and mammary gland, though α2,3-Galβ1-4 and α2,3-Galβ1-3 localization varied by tissue. These findings represent the first comprehensive spatial mapping of IAV receptors in bovine reproductive tissues and highlight potential sites for viral entry or shedding.