Diversity of mucosal immune responses in upper respiratory organs and its application for mucosal vaccine

Mucosal vaccine has been considered a promising strategy to prevent upper respiratory infections. As the immunization routes to induce mucosal immune responses, oral, intranasal, and sublingual immunizations are proposed for clinical application. Recently, it has been reported that transcutaneous immunization is also capable of inducing mucosal immune responses. However, it still remains unclear which route is the most effective to induce mucosal immune responses in upper respiratory organs. In order to investigate the differences in the immune responses among several mucosal immunizations, mice were immunized with phosphorylcholine (PC) together with cholera toxin (CT) as mucosal adjuvant intranasally, sublingually, and transcutaneously, and the mucosal as well as systemic immune responses were compared. PC-specific IgA antibody titers in saliva and nasal wash were increased by intaranasal as well as sublingual immunization to the same levels. However, IgE levels induced by mucosal immunization were remarkably reduced by sublingual immunization. Transcutaneous immunization increased mucosal IgA responses, although the levels were lower than those induced by intaranasal and sublingual immunization. Those results suggest that sublingual immunization might be superior to the other immunizations in inducing PC-specific mucosal immune responses in upper respiratory tract.