Ovalbumin-protein sigma 1 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-p sigma 1), p sigma 1 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-p sigma 1 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-p sigma 1 than those fed p sigma 1 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 beta 1 (TGF-beta 1) 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-beta 1 and IL-10 producing, CD25(+) CD4(+) regulatory T cells in both systemic and mucosal lymphoid tissues.