Although the SAa2-6Gal glycans was detected in human tracheal/bronchial goblet cells [19, 20] and was capped on mucin protein [24] , it was also proposed that tracheal mucin in the airway contains SAa2-3Gal [25] (Fig. 6A) . Especially, this secreted mucin was shown to prevent infection by influenza viruses with a SAa2-3Gal preference in the airway [26] . This false-receptor effect may mask the HA of the AIV, disable the viral access to the goblet cells and also account, at least in part, for the hindrance of AIV infection to human goblet cell [26] . In chicken trachea, goblet cells exhibit high affinity for SNA, suggesting that the mucin may contain SAa2-6Gal glycans. The viral neutralization effect of mucin in humans may be recapitulated in chickens to aid the clearance of the invading influenza viruses with a SAa2-6Gal preference.