CD4+CD25+ regulatory T cells suppress contact hypersensitivity reactions through a CD39, adenosine-dependent mechanism.
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.


CONCLUSIONS
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.
Department of Dermatology, University Hospital Heidelberg, Heidelberg, Germany.
Sabine
S
Ring
Stephen J
SJ
Oliver
Bruce N
BN
Cronstein
Alexander H
AH
Enk
Karsten
K
Mahnke
D000241:Adenosine / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism*; D001081:Apyrase / Q000235:genetics / Q000378:metabolism*; D015704:CD4 Antigens / Q000276:immunology; D002450:Cell Communication / Q000187:drug effects / Q000276:immunology; D049109:Cell Proliferation / Q000187:drug effects; D003877:Dermatitis, Contact / Q000276:immunology*; D019040:E-Selectin / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D042783:Endothelial Cells / Q000187:drug effects / Q000276:immunology; D007108:Immune Tolerance; D053645:Interleukin-2 Receptor alpha Subunit / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D019007:P-Selectin / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism; D050378:T-Lymphocytes, Regulatory / Q000187:drug effects / Q000201:enzymology / Q000276:immunology*
D015703:Antigens, CD; D015704:CD4 Antigens; D019040:E-Selectin; D053645:Interleukin-2 Receptor alpha Subunit; D019007:P-Selectin; D001081:Apyrase; C067869:CD39 antigen; D000241:Adenosine