Recombinant Bacillus subtilis spores expressing cholera toxin B and ovalbumin prevent ovalbumin-specific food allergy in mice by upregulating regulatory T cells and modulating gut microbiome flora.

BACKGROUND

Although oral immunotherapy has shown clinical efficacy in treating food allergies, its broader implementation is constrained by the occurrence of adverse effects. Consequently, inducing allergen-specific immune tolerance during early life can be a preventive strategy to reduce the development of food allergy.

OBJECTIVE

Here, we developed a novel fusion protein cholera toxin B (CTB)-ovalbumin (OVA) expressed on Bacillus subtilis (B.s-CotC-CTB-OVA) spore surface and investigated whether B.s-CotC-CTB-OVA spores prevent OVA-induced food allergy in a mouse model and explored the potential underlying mechanisms.

METHOD: Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot were used to confirm that CTB-OVA was expressed on B. subtilis spores. Female BALB/c mice were orally administered with B.s-CotC-CTB-OVA spores and B. subtilis spore control (B.s-CotC and B.s-CotC-CTB) for 4 weeks. Then, sensitization and challenge with OVA were performed on mice. Fecal OVA-secretory IgA (sIgA) and serum OVA-IgE, IgG1, and IgG2a levels were measured by enzyme-linked immunosorbent assay (ELISA). The gut microbiome was analyzed by 16S rDNA sequencing. After challenge, diarrhea score, anaphylactic reactions score, splenocyte interleukin (IL)-10, IL-4, and interferon-γ (IFN-γ), and Treg levels were measured. mRNA of IL-10, IL-4, IFN-γ, and Foxp3 were measured. Fecal microbiota transplant (FMT) was used to explore the mechanisms of microbiome in B. subtilis on food allergy.

RESULTS

Recombinant CTB-OVA was successfully expressed on the surface of B. subtilis. Oral administration of B.s-CotC-CTB-OVA can increase fecal OVA-sIgA, alleviate food allergy symptoms, and decrease serum OVA-IgE in mice with significance (p < 0.05). Moreover, oral administration of B.s-CotC-CTB-OVA can significantly reduce serum OVA-IgG1, OVA-IgG2, IL-4, spleen mast cells, and eosinophil levels and significantly increase serum IL-10 and Treg levels (p < 0.05). Additionally, microbiome analysis shows that oral administration of B.s-CotC-CTB-OVA can significantly increase the relative abundance of Muribaculaceae and significantly decrease the relative abundance of Alistipes. FMT partially reproduced the reduction in serum OVA-specific IgE, but did not significantly improve allergic symptom or diarrhea scores, suggesting that gut microbiota alterations may partially contribute to the immunological effects of B.s-CotC-CTB-OVA.

CONCLUSION

These findings suggest that B.s-CotC-CTB-OVA spores may serve as a preventive oral antigen-delivery strategy to promote antigen-specific immune regulation and partially modulate microbiota-associated immune responses in OVA-induced food allergy.