Ovalbumin-Protein σ1 M-Cell Targeting Facilitates Oral Tolerance With Reduction of Antigen-Specific CD4⁺ T Cells

Background & Aims: The follicle-associated epithelium (FAE) plays key roles in antigen uptake and subsequent induction of mucosal immunity. In this study, we examined whether M-cell targeting using a protein antigen (Ag) delivery system would induce oral tolerance instead of enhancement of Ag-specific mucosal antibody (Ab) responses. Methods: Mice were fed different doses of a recombinant protein sigma 1 of reovirus genetically conjugated to ovalbumin (OVA-pσ1), pσ1 only, or phosphate-buffered saline (PBS) before oral challenge with OVA plus cholera toxin as mucosal adjuvant. OVA-specific Ab and CD4-positive (CD4⁺) T-cell responses were determined. Results: A low dose of OVA-pσ1 reduced anti-OVA Ab and CD4⁺ T-cell responses in both mucosal and systemic lymphoid tissues. OVA/MHC I-A^d tetramer staining showed that the numbers of OVA-specific CD4⁺ T cells were significantly reduced in lamina propria of mice fed OVA-pσ1 than those fed pσ1 only or PBS only. In fact, Foxp3 expressing CD25⁺ CD4⁺ T cells were markedly increased in this tissue. Nonetheless, CD25⁺ CD4⁺ T cells from the spleen, mesenteric lymph nodes, and Peyer's patches of orally tolerized mice showed increased transforming growth factor β1 (TGF-β1) and interleukin-10 (IL-10) production compared with nontolerized mice. Conclusions: These results show that an FAE M-cell targeting protein Ag delivery system facilitates oral tolerance induction because of a reduction in Ag-specific CD4⁺ T cells and increased levels of TGF-β1 and IL-10 producing, CD25⁺ CD4⁺ regulatory T cells in both systemic and mucosal lymphoid tissues.

Abbreviations used in this paper: Ab, antibody, AFC, antibody-forming cell, Ag, antigen, APC, antigen-presenting cell, CT, native cholera toxin, Cy5.5, Cyanin5.5, DC, dendritic cell, DTH, delayed-type hypersensitivity, ELISA, enzyme-linked immunoabsorbent assay, FITC, fluorescein isothiocyanate, GALT, gut-associated lymphoreticular tissue, IFN-γ, interferon-γ, IgA, immunoglobulin A, IL-10, interleukin-10, iLP, intestinal lamina propria, mAb, monoclonal antibody, MLNs, mesenteric lymph nodes, OVA, ovalbumin, OVA-pσ1, recombinant protein sigma 1 of reovirus genetically conjugated to ovalbumin, PBS, phosphate-buffered saline, PE, phycoerythrin, PerCP, peridinin chlorophyll protein, PMA, phorbol 12-myristate 13-acetate, PP, Peyer's patch, pσ1, protein sigma 1, TGF-β1, transforming growth factor β1, Th3, T-helper type 3, Treg, T regulatory