The <i>Levilactobacillus Brevis</i> NZ3 Isolated From Fermented <i>Brassica Rapa</i> L. Induces IL‐15 Production in Dendritic Cells via Inducing IFN‐α

Interleukin-15 (IL-15) is a potential adjuvant in the activation of antitumor and antiviral immunity. Certain fermented food components possess immunomodulatory effects. We previously showed that lactic acid bacteria (LAB) isolated from Nozawana-zuke-the traditional Japanese fermented Brassica rapa L. pickle-activate immune function. Here we aimed to identify the LAB strain in fermented B. rapa L. that can markedly induce the expression of IL-15 mRNA in dendritic cells (DCs). We found that the Levilactobacillus brevis NZ3 strain isolated from B. rapa L. induces IL-15 production in DCs. We also provided mechanistic insight into the mechanism by which the NZ3 strain induces IL-15 production in DCs. We report that the NZ3 strain-induced IL-15 production in DCs is mediated by Toll-like receptor 3 signaling. Furthermore, inhibiting the interferon-α/β receptor alpha chain abrogated the NZ3 strain-induced IL-15 production. Further analysis using a Protein Kinase B (AKT) inhibitor revealed that the NZ3 strain-induced IL-15 production is mediated by AKT signaling, which occurs downstream of Interferon-α/β receptor signaling. Overall, our results indicate that the Levilactobacillus brevis NZ3 strain may serve as a potentially beneficial immunomodulatory bacterial strain. Moreover, due to its ability to induce IL-15 production, the NZ3 strain may serve as a candidate immunomodulatory strain for future studies.