Lactobacillus plantarum strain YU from fermented foods activates Th1 and protective immune responses

► In this study, we isolated a beneficial lactic acid bacterium, Lactobacillus plantarum strain YU (LpYU), from fermented foods. ► LpYU has very high IL-12-inducing activity in vitro. ► LpYU suppresses antigen-specific IgE production by activation of Th1 immune responses in mice. ► LpYU enhances natural killer cell activity and IgA production in vitro. ► LpYU has protective effects against influenza A virus infection in vivo.