Seasonal influenza continues to occur and the number of affected individuals does not seem to decrease. Kao is focusing on biological barriers that are inherent in humans and working to develop safe preventive technologies for upper respiratory tract infections, such as influenza and colds, that can be used in everyday life. One area of investigation is the function of saliva, 1 to 1.5 liters of which is secreted daily by healthy individuals. Saliva has been reported to have antibacterial and antiviral, as well as digestive, cleansing, and masticatory assisting effects.
From basic research conducted thus far, Kao has shown that the amount of protein-bound sialic acid (BSA) contained in human saliva is important for its anti-influenza virus effect. Furthermore, it has been confirmed that BSA is secreted more from the submandibular and sublingual glands (SMSL grands) (Fig. 1) than from the parotid gland ^*1. Based on this finding, it was considered that promotion of saliva secretion from the SMSL glands would be effective for preventing influenza infection.