Figure 1: The Treg regulatory pathways. (a) The ability of Tregs to induce immune suppression is mediated via (1) inhibitory cytokines; (2) induction of apoptosis by granzyme/perforin pathway; (3) CD39/CD73/adenosine pathway; (4) direct transfer of cAMP via GAP junction; (5) inhibition of DC function by CD80/CD86 and CTLA-4 interaction; and (6) the catabolism of tryptophan via IDO enzyme. (b) Dual function of HIF-1α in regulation of Treg and Th17 cells.