Determining the role of differentially linked sialic acids in H5N1 Influenza entry

Influenza A viruses pose a serious global threat due to their ability to reassort and cross the species barrier from animals to humans. These events are especially dangerous when humans are immunologically naïve to a particular influenza strain, which can result in deadly pandemics. Influenza viruses initiate entry into host cells by attaching to varying moieties of the carbohydrate, sialic acid. Avian influenza viruses, such as the H5N1 strain, bind α2-3 linked sialic acid while human influenza viruses bind to α2-6 linked sialic acid. Previous data from the lab indirectly indicates that the amount of α2-3 and/or α2-6 sialic acid does not correlate with H5N1 entry levels, suggesting that an additional co-factor may be necessary to mediate H5N1 entry. To directly investigate the involvement of α2-3 and α2-6 sialic acids in H5N1 influenza entry, a series of neutralization assays were carried out using sialic acid binding lectins. Lectins are nonenzymatic proteins which bind various carbohydrates. Sambucus nigra lectin binds to α2-6 sialic acid whereas Maackia amurensis lectin II binds to α2-3 sialic acid. To examine the role of α2-3 and α2-6 sialic acids in H5N1 entry, A549 human lung epithelial cells were pre-incubated with increasing concentrations of each lectin and challenged with the H5N1 virus. Preliminary data demonstrates that even at concentrations of 1mg/ml of either lectin, H5N1 is still able to mediate entry. This data is consistent with previous studies, suggesting that sialic acid is not the only receptor for H5N1 and that an additional co-factor may be necessary.