NOS2 and cystic fibrosis: Interestingly, studies by Grasemann and colleagues showed that patients with CF have a decreased concentration of exhaled NO (Grasemann et al., 1997), related to decreased nitric-oxide synthase (iNOS) activity, increased cellular arginase activity, and decreased arginine bioavailability (Grasemann et al., 2011; Grasemann and Ratjen, 2012; Grasemann et al., 2005).