Abstract
Oral immunization with a Salmonella vaccine vector expressing enterotoxigenic Escherichia coli colonization factor Ag I (CFA/I) can protect against collagen-induced arthritis (CIA) by dampening IL-17 and IFN-γ via enhanced IL-4, IL-10, and TGF-β. To identify the responsible regulatory CD4(+) T cells making the host refractory to CIA, Salmonella-CFA/I induced CD39(+)CD4(+) T cells with enhanced apyrase activity relative to Salmonella vector-immunized mice. Adoptive transfer of vaccine-induced CD39(+)CD4(+) T cells into CIA mice conferred complete protection, whereas CD39(-)CD4(+) T cells did not. Subsequent analysis of vaccinated Foxp3-GFP mice revealed the CD39(+) T cells were composed of Foxp3-GFP(-) and Foxp3-GFP(+) subpopulations. Although each adoptively transferred Salmonella-CFA/I-induced Foxp3(-) and Foxp3(+)CD39(+)CD4(+) T cells could protect against CIA, each subset was not as efficacious as total CD39(+)CD4(+) T cells, suggesting their interdependence for optimal protection. Cytokine analysis revealed Foxp3(-) CD39(+)CD4(+) T cells produced TGF-β, and Foxp3(+)CD39(+)CD4(+) T cells produced IL-10, showing a segregation of function. Moreover, donor Foxp3-GFP(-) CD4(+) T cells converted to Foxp3-GFP(+) CD39(+)CD4(+) T cells in the recipients, showing plasticity of these regulatory T cells. TGF-β was found to be essential for protection because in vivo TGF-β neutralization reversed activation of CREB and reduced the development of CD39(+)CD4(+) T cells. Thus, CD39 apyrase-expressing CD4(+) T cells stimulated by Salmonella-CFA/I are composed of TGF-β-producing Foxp3(-) CD39(+)CD4(+) T cells and support the stimulation of IL-10-producing Foxp3(+) CD39(+)CD4(+) T cells.