Postbiotic Lactobacillus sakei CVL-001 promotes mucosal tolerance via NOD2-dependent programming of tolerogenic CD11c+ antigen-presenting cells.

Postbiotics offer improved safety and stability over live probiotics for modulating intestinal immunity, yet the receptor-mediated mechanisms underlying mucosal tolerance remain unclear. Nucleotide-binding oligomerization domain 2 (NOD2), a cytosolic sensor of bacterial cell wall components and a major genetic risk factor for inflammatory bowel disease (IBD), may link microbial signals to regulatory immune programs. Here, we show that heat-killed Lactobacillus sakei CVL-001 (HK CVL-001) promotes intestinal homeostasis through NOD2 signaling. HK CVL-001, but not its culture supernatant, significantly alleviated dextran sulfate sodium (DSS)-induced colitis, whereas this protection was completely lost in NOD2-/- mice. Treatment suppressed pro-inflammatory cytokines (IL-6, IL-1β), increased IL-10, and expanded Foxp3+ regulatory T cells (Tregs) and CD103+ tolerogenic antigen-presenting cell (APC) populations. In vitro, HK CVL-001 directly induced CD103 expression in BMDCs in a NOD2-dependent manner, enhancing their capacity to drive Treg differentiation. This effect was accompanied by upregulation of Irf8 and Irf4, along with expansion of both CD11b- and CD11b+ CD103+ APC populations. A functional role for NOD2 signaling within CD11c+ APCs was confirmed using CD11c-Cre × NOD2fl/fl mice and adoptive transfer experiments. These findings support a NOD2-dependent CD11c+ APC-Treg regulatory axis underlying postbiotic-induced mucosal tolerance.