AR and allergic asthma: Adenosine levels increase in the lungs of patients with allergic asthma, which contributes to bronchoconstriction and mast cell degranulation.17 A2A AR agonists, as well as A1 AR, A2B AR, and A3 AR antagonists, show anti‐asthmatic effects by reducing inflammation, bronchoconstriction and mucus secretion in animal models.18 A2B AR and A3 AR have been evaluated as important targets in the development of drugs for asthma treatment because of safety issues with other ARs.19, 20