Sublingual administration of Lactobacillus rhamnosus affects respiratory immune responses and facilitates protection against influenza virus infection in mice.

The extensive morbidity and mortality caused by influenza A viruses worldwide prompts the need for a deeper understanding of the host immune response and novel therapeutic and/or prophylactic interventions. In this study, we assessed the sublingual route as an effective means of delivering probiotics against influenza virus in mice. In addition, IgA levels, NK cell activity, T cell activation, and cytokine profiles in the lungs were examined to understand the mechanism underlying this protective effect. Sublingual administration of Lactobacillus rhamnosus provided enhanced protection against influenza virus infection by enhancing mucosal secretory IgA production, and T and NK cell activity. Moreover, interleukin (IL)-12 levels in the lungs increased significantly. Conversely, IL-6 and tumor necrosis factor alpha levels in the lungs decreased significantly. On the basis of these promising findings, we propose that the sublingual mucosal route is an attractive alternative to mucosal routes for administering probiotics against influenza virus. Crown