Reviews and feature article
CD4+CD25+ regulatory T cells suppress contact hypersensitivity reactions through a CD39, adenosine-dependent mechanism

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Background

Injection of regulatory T (Treg) cells into sensitized mice abrogates the elicitation phase of contact hypersensitivity (CHS) reactions by blocking the adherence of leukocytes to vascular endothelium.

Objective

We set out to analyze whether adenosine, a suppressive factor recently described as produced by Treg cells, can account for the suppression of the effector T-cell–endothelial cell (EC) interaction.

Methods

T cells and ECs were cultured in the presence of adenosine, and expression of adhesion molecules and adhesion of T cells to ECs under shear stress were assessed. Furthermore, we injected Treg cells derived from ectonucleotidase-deficient (CD39−/−) mice into sensitized mice and analyzed the sticking and rolling of leukocytes during a CHS response using intravital microscopy.

Results

Adenosine or Treg cells, respectively, abrogated the adherence of effector T cells to ECs in vitro. Likewise, injection of adenosine and Treg cells abrogated the ear-swelling reaction, indicating a role of adenosine during Treg cell–induced suppression of CHS responses. As a source for Treg cell–derived adenosine, we identified the ectonucleotidase CD39 because CD39-deficient Treg cells did not prevent adhesion of leukocytes to the endothelium. Furthermore, we show that the impaired adhesion of effector T cells to inflamed endothelium was induced by adenosine-mediated downregulation of expression of E- and P-selectin on the vascular endothelium.

Conclusion

Adenosine release by Treg cells is essential to block leukocyte adhesion to endothelium, providing a novel mechanism by which Treg cells mediate immune suppression in vivo.

Section snippets

Mice

BALB/c and C57BL/6 mice originally purchased from Charles River (Sulzfeld, Germany) were housed at the central animal facility of the University of Heidelberg and cared for in accordance with the institutional guidelines for animal welfare. CD39−/− mice were housed in the animal facility of New York University according to respective institutional guidelines.

Reagents and antibodies

The CD4+CD25+ Regulatory T Cell Isolation Kit and CD8 MicroBeads were purchased from Miltenyi Biotec (Bergisch Gladbach, Germany);

Adenosine blocks the ear-swelling reaction in vivo and abrogates T-cell proliferation in mixed leukocyte reactions in vitro

Because we and others have shown that Treg cells suppress the challenge phase of CHS reactions, we set out to investigate whether adenosine is involved in this process. During initial experiments, we injected Treg cells or adenosine into TNCB-sensitized mice before challenge and found that Treg cells and adenosine were independently able to suppress the ear-swelling reaction induced by challenge (Fig 1, A). Moreover, theophylline, an adenosine receptor antagonist, prevented the suppressive

Discussion

In this study we found that Treg cell–derived adenosine plays a major role in preventing the elicitation of CHS reactions by blocking the interaction of effector T cells with the vascular endothelium. The well-documented anti-inflammatory effects of adenosine have earned it the description of “retaliatory metabolite,”14 with reported suppressive effects, including direct inhibition of colitis and ileitis,15, 16 amelioration of type I diabetes,17 stimulation of IL-10 release by macrophages,18

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    • Cited by (0)

    Supported by grants to K. Mahnke and A. H. Enk (SFB 405 B15, B16; DFG KM 1924/2-2; the Wilhelm Sander Foundation; European Union grant LSHC-CT-2005-518178 and the Helmholtz Association: Alliance on Immunotherapy of Cancer). S. J. Oliver and B. N. Cronstein were supported by grants from the National Institutes of Health (GM56268, AR41911, AA13336, 5K23AR2187, 1R21HL077461, and 5R21NS048594), King Pharmaceuticals, the General Clinical Research Center (M01RR00096), and the Kaplan Cancer Center.

    Disclosure of potential conflict of interest: S. J. Oliver has received research support from Celgene Corporation. B. N. Cronstein owns the patents on the use of adenosine A2A receptor antagonists to promote wound healing and the use of A2A receptor antagonists to inhibit fibrosis, the patent on the use of adenosine A1 receptor antagonists to treat osteoporosis and other bone diseases, the patent on the use of adenosine A1 A2B receptor antagonists to treat fatty liver, and the patent on the use of adenosine A2A receptor antagonists to prevent prosthesis loosening; has served as a consultant for Cypress Bioscience, King Pharmaceuticals, CanFite Biopharmaceuticals, Bristol-Myers Squibb, Celizome, Tap Pharmaceuticals, Prometheus Laboratories, Regeneron, Sepracor, Amgen, Endocyte, Protalex, Allos, Combinatorx, Kyowa Hakka, Hoffman-LaRoche, Savient, and Avidimer Therapeutics; owns stock in CanFite Biopharmaceuticals; has received grants from King Pharmaceuticals, the National Institutes of Health, and the Vilcek Foundation; and is a board member for the Vilcek Foundation. The rest of the authors have declared that they have no conflict of interest.

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