Preventive effect of heat-killed Lactiplantibacillus plantarum FM8 in an ovalbumin-induced food allergy murine model

Background: Paraprobiotics, the non-viable microbial cells with health benefits, have gained interest as candidates for preventing food allergies owing to their safety and stability. Heat-killed Lactiplantibacillus plantarum FM8 (FM8) has been reported to induce interleukin (IL)-10 production in dendritic cells in vitro; however, its in vivo efficacy as a standalone intervention remains unexplored. We investigated the preventive effect of heat-killed FM8 in a murine model of ovalbumin (OVA)-induced food allergy. Methods: BALB/c mice were assigned to control, OVA-induced allergy, or three FM8 treatment groups receiving FM8 at low (2 × 10⁹ CFU/day), medium (1 × 10¹⁰ CFU/day), or high (5 × 10¹⁰ CFU/day) doses. Food allergy was induced by repeated OVA sensitization and challenge. Allergy symptoms, OVA-specific immunoglobulin E (IgE), and IL-10 levels were measured. Tight junction gene expression, mucin production, gut microbiota composition, and short-chain fatty acids (SCFAs) were also analyzed. Results: FM8 supplementation attenuated allergic responses in a dose-dependent manner. Allergy symptom scores were reduced in the High group, and the rectal temperature decline following OVA challenge was ameliorated in both the Med and High groups. The sensitization-induced increase in OVA-specific IgE was also attenuated in these groups. IL-4 expression in Peyer’s patches was reduced, whereas colonic IL-10 expression and serum IL-10 levels were increased in the High group. FM8 supplementation was further associated with increased ileal expression of tight junction-related genes (Occludin, Claudin-1 and Zo-1) and Muc2, along with a trend toward increased fecal mucin levels; however, no comparable changes in tight junction-related gene expression were observed in the colon. Although taxa with reported SCFA-producing potential were enriched in the High group, cecal acetate and propionate levels remained unchanged, while butyrate levels were decreased. Conclusions: FM8 may prevent food allergy by promoting IL-10-associated immunoregulation and enhancing gut barrier-related responses, without a corresponding increase in cecal SCFA concentrations. The contribution of SCFA-related mechanisms remains to be clarified, and further studies are needed to determine clinically feasible dosing and efficacy in humans.