The quail and chicken intestine have
sialyl-galactose sugar chains responsible
for the binding of influenza A viruses to human type receptors
Received on October 12, 2006; revised on March 13, 2007; accepted on March 22, 2007
The receptor specificity of influenza viruses is one factor that allows avian influenza viruses to cross the species barrier. The recent transmissions of avian H5N1 and H9N2 influenza viruses from chickens and/or quails to humans indicate that avian influenza viruses can directly infect humans without an intermediate host, such as pigs. In this study, we used two strains of influenza A virus (A/PR/8/34, which preferentially binds to an avian-type receptor, and A/Memphis/1/71, which preferentially binds to a human-type receptor) to probe the receptor specificities in host cells. Epithelial cells of both quail and chicken intestines (colons) could bind both avian- and human-type viruses. Infected cultured quail colon cells expressed viral protein and allowed replication of the virus strain A/PR/8/34 or A/Memphis/1/71. To understand the molecular basis of these phenomena, we further investigated the abundance of sialic acid (Sia) linked to galactose (Gal) by the 2-3 linkage (Sia2-3Gal) and Sia2-6Gal in host cells. In glycoprotein and glycolipid fractions from quail and chicken colon epithelial cells, there were some bound components of Sia–Gal linkage-specific lectins, Maackia amurensis agglutinin (specific for Sia2-3 Gal) and Sambucus nigra agglutinin (specific for Sia2-6Gal), indicating that both Sia2–3Gal and Sia2-6Gal exist in quail and chicken colon cells. Furthermore, we demonstrated by fluorescence high-performance liquid chromatography (HPLC) analysis that 5-N-acetylneuraminic acid was the main molecular species of Sia, and we demonstrated by multi-dimensional HPLC mapping and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis that bi-antennary complex-type glycans 2-6 sialylated at the terminal Gal residue(s) are major (more than 79%) sialyl N-glycans expressed by intestinal epithelial tissues in both the chicken and quail. Taken together, these results indicate that quails and chickens have molecular characterization as potential intermediate hosts for avian influenza virus transmission to humans and could generate new influenza viruses with pandemic potential.