In parallel to the studies of GSH in immunity, more complex molecular and biochemical studies have pointed out a regulatory role of GSH. This was a result of an evolution from the concept of oxidative stress outlined above to that of redox regulation. The concept of redox regulation implies that some oxidative changes (such as changes in the redox state of protein cysteines) are not necessarily damaging but can have regulatory properties. While this idea shows a more complex picture from the popular one where free radicals and oxidants are bad and antioxidants are good, it implies that GSH is an essential molecule not only in acting as an antioxidant but also in the absence of oxidative stress, as an endogenous signaling molecule. The molecular mechanisms of GSH-mediated redox regulation are being actively investigated and have in part been identified. [87] [88] [89] Although the present review focused on the immuno pathogenesis of pulmonary diseases, the key concepts outlined here may help in interpreting the role of redox in other pathological conditions.