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Classical neurotransmitters such as monoamines and acetylcholine regulate the magnitude and quality of immune responses (1-4). The recent discovery of interleukin-17 (IL-17)-producing [T.sub.H]17 cells as a distinct subset of effector [...], High amounts of glutamate are found in the brains of people with multiple sclerosis, an inflammatory disease marked by progressive demyelination. Glutamate might affect neuroinflammation via effects on immune cells. Knockout mice lacking metabotropic glutamate receptor-4 (mGluR4) were markedly vulnerable to experimental autoimmune encephalomyelitis (EAE, a mouse model of multiple sclerosis) and developed responses dominated by interleukin-17-producing T helper ([T.sub.H]17) cells. In dendritic cells (DCs) from those mice, defective mGluR4 signaling--which would normally decrease intracellular cAMP formation--biased [T.sub.H] cell commitment to the [T.sub.H]17 phenotype. In wild-type mice, mGluR4 was constitutively expressed in all peripheral DCs, and this expression increased after cell activation. Treatment of wild-type mice with a selective mGluR4 enhancer increased EAE resistance via regulatory T ([T.sub.reg]) cells. The high amounts of glutamate in neuroinflammation might reflect a counterregulatory mechanism that is protective in nature and might be harnessed therapeutically for restricting immunopathology in multiple sclerosis.

Glucocorticoid-induced tumor necrosis factor receptor (GITR) on T cells and its natural ligand, GITRL, on accessory cells contribute to the control of immune homeostasis. Here we show that reverse signaling through GITRL after engagement by soluble GITR initiates the immunoregulatory pathway of tryptophan catabolism in mouse plasmacytoid dendritic cells, by means of noncanonical NF-[kappa]B-dependent induction of indoleamine 2,3-dioxygenase (IDO). The synthetic glucocorticoid dexamethasone administered in vivo activated IDO through the symmetric induction of GITR in CD4[sup.+] T cells and GITRL in plasmacytoid dendritic cells. The drug exerted IDO-dependent protection in a model of allergic airway inflammation. Modulation of tryptophan catabolism via the GITR-GITRL coreceptor system might represent an effective therapeutic target in immune regulation. Induction of IDO could be an important mechanism underlying the anti-inflammatory action of corticosteroids., Author(s): Ursula Grohmann [1]; Claudia Volpi [1]; Francesca Fallarino [1]; Silvia Bozza [1]; Roberta Bianchi [1]; Carmine Vacca [1]; Ciriana Orabona [1]; Maria L Belladonna [1]; Emira Ayroldi [2]; Giuseppe [...]