Figure 10: Sympathetic regulation of Th17 and Treg cell balance. Th0 and Treg cells express β2-ARs, however, whether Th17 express this receptor has not been determined. APCs also express β2-ARs. These receptors provide a direct mechanism by which the SNS regulates Th cell differentiation and Treg effector cell function. NE released from sympathetic nerves binds with β2-ARs expressed on the cell surface of Th0 and APCs mediate SNS regulation of Th17 and Treg cell differentiation. Under normal conditions, the SNS drives the differentiation of Th17 cells by increasing the production of IL-6 and TGF-β by APCs. In contrast, activation of β2-ARs in Th0 cells inhibits Treg cell differentiation by reducing IL-2. Further, downstream signaling pathways of β2-AR in Treg cells, inhibit effects of TGF-β by suppression TGF-β-induced activation of ERK- and JNK pathways. (Green arrows, excitatory; red arrows, inhibitory).