Enterococcus casseliflavus KB1733 Isolated from a Traditional Japanese Pickle Induces Interferon-Lambda Production in Human Intestinal Epithelial Cells

The association between lactic acid bacteria (LAB) and their immunostimulatory effects has attracted considerable attention; however, it remains unclear whether LAB can induce interferon-lambdas (IFN-lambda s) in human epithelial cells under conditions that do not mimic infection. In this study, we first employed a reporter assay to screen for a potential strain capable of inducing IFN-lambda 3 among 135 LAB strains derived from traditional Japanese pickles. Next, we assessed the strain's ability to induce the expression of IFN-lambda genes and interferon-stimulated genes (ISGs), and to produce IFN-lambda s. As a result, we screened and isolated Enterococcus casseliflavus KB1733 (KB1733) as a potential strain capable of inducing IFN-lambda 3 expression. Furthermore, we clarified that KB1733 induced the expression of IFN-lambda genes and ISGs related to antiviral functions, and that KB1733 induced IFN-lambda 1 and -lambda 3 expression in a dose-dependent manner up to 10 mu g/mL. In addition, KB1733 significantly increased IFN-lambda 1 production compared to Enterococcus casseliflavus JCM8723(T), which belongs to the same genera and species as KB1733. In conclusion, we isolated a unique LAB strain from traditional Japanese pickles that is capable of stimulating IFN-lambda production, although further study is needed to investigate how KB1733 protects against viruses in mice and humans.