Increased levels of α2-3- and α2-6-linked sialic acids during airway inflammation govern influenza A binding to peripheral airway mucins in a subtype-dependent manner

Background Influenza infection increases the risk of pneumonia and respiratory failure in chronic obstructive pulmonary disease (COPD) and mucins play an important role in pulmonary host defense. Methods Lower airway mucins were obtained from long-term smokers with and without COPD, pneumonia patients, and healthy never-smokers; oral MUC5B was obtained from a healthy never-smoker, and the ability of lower airway mucins and oral MUC5B to bind influenza A virus (H1N1 and H3N2) was investigated. Results Lower airway mucins from long-term smokers with and without COPD, as well as the oral MUC5B, bound to H1N1. In contrast, all mucins, regardless of donors, bound to H3N2. Differences in binding were linked to more pronounced glycan sialylation in lower airway mucins from pneumonia patients and long-term smokers compared with healthy never-smokers. For lower airway mucins, the abundance of α2-6-linked NeuAc correlated with H1N1 binding, whereas the abundance of α2-3-linked NeuAc correlated with H3N2 binding. A neuraminidase inhibitor increased virus binding, even more so for H1N1 than for H3N2, resulting in the binding of both H1N1 and H3N2 to all mucins. The H1N1 neuraminidase cleaved α2-3- and α2-6-linked NeuAc to a similar degree, whereas the H3N2 neuraminidase mainly cleaved the α2-6-linked NeuAc. Mucins inhibited influenza A infection in a concentration-dependent manner in airway epithelial cells, although more so for H1N1 than for H3N2. Conclusion Mucins inhibit influenza infection, and this effect depends on viral subtype. Neuraminidase inhibitors enable mucins with low sialic acid content to preserve their virus-binding ability, thereby underscoring their therapeutic potential.