The role of iNOS in asthma is controversial as it has been reported that the degree of OVA-evoked airway inflammation is less in iNOS-KO mice than in WT mice [65], whereas a comparable degree of OVA-evoked airway hyperresponsiveness in iNOS-KO and WT mice has also been indicated [64]. Here, NOS2 is linked to airway hyperresponsiveness.