Attenuation of Chronic Pulmonary Inflammation in A2B Adenosine Receptor Knockout Mice

Pharmacologic evidence suggests that activation of A(2B) adenosine receptors results in proinflammatory effects relevant to the progression of asthma, a chronic lung disease associated with elevated interstitial adenosine concentrations in the lung. This concept has been challenged by the finding that genetic removal of An receptors leads to exaggerated responses in models of acute inflammation. Therefore, the goal of our study was to determine the effects of A(2B) receptor gene ablation in the context of ovalbumin-induced chronic pulmonary inflammation. We found that repetitive airway allergen challenge induced a significant increase in adenosine levels in fluid recovered by bronchoalveolar lavage. Genetic ablation of A(2B) receptors significantly attenuated allergen-induced chronic pulmonary inflammation, as evidenced by a reduction in the number of bronchoalveolar lavage eosinophils and in peribronchial eosinophilic infiltration. The most striking difference in the pulmonary inflammation induced in A(2B) receptor knockout (A(2B)KO) and wildtype mice was the lack of allergen-induced IL-4 release in the airways of A(2B)KO animals, in line with a significant reduction in IL-4 protein and mRNA levels in lung tissue. In addition, attenuation of allergen-induced transforming growth factor-beta release in airways of A(2B)KO mice correlated with reduced airway smooth muscle and goblet cell hyperplasia/hypertrophy. In conclusion, genetic removal of A(2B) adenosine receptors in mice leads to inhibition of allergen-induced chronic pulmonary inflammation and airway remodeling. These findings are in agreement with previous pharmacologic studies suggesting a deleterious role for A(2B) receptor signaling in chronic lung inflammation.