Figure 12: Cyclic AMP-mediated regulation of Th cells by Treg cells. Treg cells express high levels of cAMP compared with other Th cell subsets. Cyclic AMP generally suppresses Th cell functions. One mechanism in which Treg cells suppress effector Th cells is by the transfer of cAMP to other Th cell subsets via gap junctions. The mRNA, miR-142-3p, regulates the upper limits of cAMP expression in Treg cells (cell on the left) by targeting adenylate cyclase (AC) [9]. Greater transcription of miR-142-3p inhibits AC9 activity. FoxP3 downregulates miR-142-3p transcription, which disinhibits AC9 activity to increase cAMP levels in Treg cells. In contrast, miR-142-3p inhibits AC9 expression in other T cell subsets (shown on the right), which reduces cAMP production. (Green arrows, excitatory; red arrows, inhibitory).