Oral Escherichia coli Colonization Factor Antigen I Fimbriae Ameliorate Arthritis via IL-35, Not IL-27

Abstract

A Salmonella therapeutic expressing enterotoxigenic Escherichia coli colonization factor Ag I (CFA/I) fimbriae protects against collagen-induced arthritis (CIA) by eliciting two regulatory T cell (Treg) subsets: TGF-β–producing Foxp3−CD39+CD4+ T cells and IL-10–producing Foxp3+CD39+CD4+ T cells. However, it is unclear whether CFA/I fimbriae alone are protective and whether other regulatory cytokines are involved, especially in the context for the EBI3-sharing cytokines, Treg-derived IL-35 and APC-derived IL-27, both capable of suppressing Th17 cells and regulating autoimmune diseases. Subsequent evaluation revealed that a single oral dose of purified, soluble CFA/I fimbriae protected against CIA as effectively as did Salmonella-CFA/I and found that Foxp3+CD39+CD4+ T cells were the source of secreted IL-35, whereas IL-27 production by CD11c+ cells was inhibited. Inquiring into their relevance, CFA/I fimbriae–treated IL-27R–deficient (WSX-1−/−) mice were equally protected against CIA as were wild-type mice, suggesting a limited role for IL-27. In contrast, CFA/I fimbriae–mediated protection was abated in EBI3−/− mice, accompanied by the loss of TGF-β– and IL-10–producing Tregs. Adoptive transfer of C57BL/6 CD39+CD4+ T cells to EBI3−/− mice with concurrent CFA/I plus IL-35 treatment effectively stimulated Tregs suppressing proinflammatory collagen II–specific Th cells. In contrast, recipients cotransferred with C57BL/6 and EBI3−/− CD39+CD4+ T cells and treated with CFA/I plus IL-35 were not protected, implicating the importance of endogenous IL-35 for conferring CFA/I-mediated protection. Thus, CFA/I fimbriae stimulate IL-35 required for the coinduction of TGF-β and IL-10.