NOS2 and asthma: External stimuli such as allergen exposure, cigarette smoke, traffic exhaust and folate rich diet cause methylation mediated silencing of genes like IFNγ, Fox-P3, IL2, iNOS and hypomethylation mediated activation of genes like IL6, IL4, IL8, and Acyl CoA thus increasing the Th2 phenotype assisting in the development of asthma (Durham et al., 2011).