Th178 - TGF-β3 Induces Oral Tolerance by Imprinting Gut-Homing Capacity in Regulatory T Cells

Abstract Text: Immune responses against ingested proteins are avoided by a poorly understood mechanism known as oral tolerance (OT). In a previous study, we demonstrated that OT depends on TGF-β3 but occurs in the absence of TGF-β1. Here, we sought the cellular source of TFG-β3 during OT and analyzed the mechanism through which it induces the process.
We used conditional knockout mice (cKO) to identify the cellular lineages that produce TGF-β3 during OT. We used ovalbumin (OVA) as a model antigen and OT-II FoxP3GFP cells to analyze Treg generation. OT was tested in a model of delayed-type hypersensitivity and anti-OVA antibodies were quantified.
Conditional deletion of Tgfb3 in all cell lineages (Tamoxifen-Cre) abolished OT and enhanced anti-OVA antibody production. Deletion of Tgfb3 in hematopoietic cells (iVav-Cre) significantly impaired OT. Deletion of Tgfb3 in CD11c+, TCR-αβ+ (CD4-Cre), and TCR-γδ+ cells had no effect. Transcriptomic comparison of CD4 cells activated with TGF-β1 vs. TGF-β3 revealed that TGF-β3 promotes the expression of gut-homing molecules. This was confirmed using adoptively transferred OT-II cells, as OVA-specific Tregs were significantly less abundant in the small intestine lamina propria (siLP) in Tgfb3 cKO mice and expressed lower levels of CD103 and α4β7 integrin. Accordingly, during steady state, lack of TGF-β3 decreased the abundance of siLP Tregs and their expression levels of FoxP3, CD103, and α4β7 integrin.
In conclusion, TGF-β3 produced mainly by hematopoietic cells is essential for oral tolerance. This cytokine imprints Tregs with an adhesion molecule expression profile necessary for their correct functionality in the gut.