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Extracellular adenosine production is essential for Treg‐mediated Th cell suppression

Background: Adenosine is an important inflammatory mediator that suppresses proliferation and cytokine production in helper T cells (Th). Two enzymes, CD39 and CD73, expressed on the surface of several cell types including Treg, synthesize adenosine. Expression of these enzymes on Tregs is suggested to play a role in their suppressive ability. Methods: In order to determine whether CD73 activity is involved in Treg‐mediated suppression, we assessed the ability of Treg from CD73−/− mice to suppress proliferation of wildtype and CD73−/− effector T cells (Teff) in vitro. Cytokine expression was examined in Th cells from wildtype and CD73−/− mice stimulated in vitro. To test the function of CD73 on Treg in vivo, Treg from CD73−/− mice were adoptively transferred with wildtype Teff into RAG1−/− recipients. Results: CD73−/− Treg were unable to suppress proliferation of either wildtype or CD73−/− effector T cells in vitro. In addition, production of inflammatory cytokines by CD73−/− Th cells was significantly greater than wildtype. Adoptive transfer of Treg from CD73−/− mice attenuated colitis to a lesser degree than wildtype Treg. Conclusions: These data indicate that extracellular adenosine production by CD73 plays an important role in suppressing Th cell proliferation and inflammatory cytokine production in vitro and inflammation in vivo. Supported by NIH R21 AI069880 and T32 AI007496‐12.