Nitric oxide dependent signaling via cyclic GMP in dendritic cells regulates migration and T-cell polarization.

Allergic airway inflammation is accompanied by excessive generation of nitric oxide (NO). Beside its detrimental activity due to the generation of reactive nitrogen species, NO was found to modulate immune responses by activating the NO-sensitive Guanylyl Cyclases (NO-GCs) thereby mediating the formation of the second messenger cyclic GMP (cGMP). To investigate the contribution of the key-enzyme NO-GC on the development of Th2 immunity in vivo, we sensitized knock-out (KO) mice of the major isoform NO-GC1 to the model allergen ovalbumin (OVA). The loss of NO-GC1 attenuates the Th2 response leading to a reduction of airway inflammation and IgE production. Further, in vitro-generated OVA-presenting DCs of the KO induce only a weak Th2 response in the WT recipient mice upon re-exposure to OVA. In vitro, these NO-GC1 KO BMDCs develop a Th1-polarizing phenotype and display increased cyclic AMP (cAMP) formation, which is known to induce Th1-bias. According to our hypothesis of a NO-GC1/cGMP-dependent regulation of cAMP-levels we further demonstrate activity of the cGMP-activated cAMP-degrading phosphodiesterase 2 in DCs. Herewith, we show that activity of NO-GC1 in DCs is important for the magnitude and bias of the Th response in allergic airway disease most likely by counteracting intracellular cAMP.