The small intestine epithelium exempts Foxp3+ Tregs from their IL-2 requirement for homeostasis and effector function
Praveen Prakhar, Jaylene Alvarez-DelValle, Hilary Keller, Assiatu Crossman, Xuguang Tai, Yoo Kyoung Park, Jung-Hyun Park
Praveen Prakhar, Jaylene Alvarez-DelValle, Hilary Keller, Assiatu Crossman, Xuguang Tai, Yoo Kyoung Park, Jung-Hyun Park
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Research Article Immunology

The small intestine epithelium exempts Foxp3+ Tregs from their IL-2 requirement for homeostasis and effector function

Abstract

Foxp3+ Tregs are potent immunosuppressive CD4+ T cells that are critical to maintain immune quiescence and prevent autoimmunity. Both the generation and maintenance of Foxp3+ Tregs depend on the cytokine IL-2. Hence, the expression of the IL-2 receptor α-chain (CD25) is not only considered a specific marker, but also a nonredundant requirement for Tregs. Here, we report that Foxp3+ Tregs in the small intestine (SI) epithelium, a critical barrier tissue, are exempt from such an IL-2 requirement, since they had dramatically downregulated CD25 expression, showed minimal STAT5 phosphorylation ex vivo, and were unable to respond to IL-2 in vitro. Nonetheless, SI epithelial Tregs survived and were present at the same frequency as in other lymphoid organs, and they retained potent suppressor function that was associated with high levels of CTLA-4 expression and the production of copious amounts of IL-10. Moreover, adoptive transfer experiments of Foxp3+ Tregs revealed that such IL-2–independent survival and effector functions were imposed by the SI epithelial tissue, suggesting that tissue adaptation is a mechanism that tailors the effector function and survival requirements of Foxp3+ Tregs specific to the tissue environment.

Authors

Praveen Prakhar, Jaylene Alvarez-DelValle, Hilary Keller, Assiatu Crossman, Xuguang Tai, Yoo Kyoung Park, Jung-Hyun Park

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Figure 4

Tissue adaptation of adoptively transferred Foxp3+ Tregs in SI IELs.

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Tissue adaptation of adoptively transferred Foxp3+ Tregs in SI IELs. (A)...
(A) Adoptive transfer of Foxp3+ Tregs. Naive CD4+ T cells from Foxp3-GFP reporter mice (CD45.2+) were induced to differentiate into Foxp3+ Tregs in vitro and coinjected with freshly purified naive CD4+ T cells from congenic mice at a 1:4 ratio into Rag2-deficient recipient mice. Eight weeks after transfer, donor T cells were recovered from the LN and SI epithelium of host mice and assessed for Treg phenotypes after gating based on the CD45.2+ congenic marker. (B) Foxp3-GFP and CD25 expression was assessed in in vitro–differentiated naive CD4+ T cells stimulated with anti-TCR antibodies in the presence of IL-2 and TGF-β. The results are representative of 3 independent experiments. (C) In vitro–generated Foxp3+ iTregs were assessed for the expression of the indicated surface molecules. The results are representative of 2 independent experiments. (D) Histograms show CD25 and CD122 expression on Foxp3-GFP+ donor T cells from recipient LN and IEL populations (top). Graphs show the ΔMFI of CD25 and CD122 expression (bottom). The histograms are representative, and the graphs show the summary of 3 adoptive transfer experiments with a total of 6 host mice. (E) Foxp3-GFP reporter expression (top) and ΔMFI of Foxp3-GFP (bottom) in donor Foxp3-GFP+CD4+ Tregs from LN and IELs of Rag2–/– recipient mice. The histogram is representative, and the graph shows a summary of 3 adoptively transferred host mice. (F) Intracellular staining for CTLA-4 (top) and ΔMFI of CTLA-4 expression (bottom) in Foxp3-GFP+CD4+ donor T cells from LN and IELs of Rag2–/– recipient mice. The histogram is representative, and the graph shows the summary from 3 adoptive transfer experiments. (G) Surface staining for GITR and Neuropilin-1 (top) and ΔMFI of GITR and Neuropilin-1 expression (bottom) in Foxp3-GFP+CD4+ donor T cells from LN and IELs of Rag2–/– recipient mice. The histogram is representative, and the graph shows the summary from 3 adoptive transfer experiments. The data are represented as the mean ± SEM. P values were determined by paired Student’s t test. *P < 0.05, **P < 0.01, ***P < 0.001.