To better understand influenza virus
infection of pigs, we examined primary swine respiratory epithelial cells (SRECs, the primary target cells of influenza viruses in vivo), as a model system. Glycomic profiling of SRECs by mass spectrometry revealed a diverse range of
glycans terminating in
sialic acid or GalαGal. In terms of sialylation, α2-6 linkage was more abundant than α2-3, and NeuAc was more abundant than NeuGc. Virus binding and
infection experiments were conducted to determine functionally important
glycans for influenza virus
infection, with a focus on recently emerged swine viruses.
Infection of SRECs with swine and human viruses resulted in different infectivity levels.
Glycan microarray analysis with a high infectivity "triple reassortant" virus ((A/Swine/MN/593/99 (H3N2)) that spread widely throughout the North American swine population and a lower infectivity human virus isolated from a single pig (A/Swine/ONT/00130/97 (H3N2)) showed that both viruses bound exclusively to
glycans containing NeuAcα2-6, with strong binding to sialylated
polylactosamine and sialylated N-
glycans. Treatment with
mannosamine precursors of
sialic acid (to alter NeuAc/NeuGc abundances) and linkage-specific sialidases prior to
infection indicated that the influenza viruses tested preferentially utilize NeuAcα2-6-sialylated
glycans to infect SRECs. Our data indicate that NeuAcα2-6-terminated
polylactosamine and sialylated N-
glycans are important determinants for influenza viruses to infect SRECs. As NeuAcα2-6
polylactosamine glycans play major roles in human
virus infection, the importance of these receptor components in
virus infection of swine cells has implications for transmission of viruses between humans and pigs and for pigs as possible adaptation hosts of novel
human influenza viruses.