Adenosine has been suggested to play a role in chronic inflammatory lung diseases such as asthma and COPD. The human lung fibroblast (HLF) is one of the major effector cells involved in chronic lung inflammation. The goal this study was to determine the expression and function of adenosine receptors (AdoRs) in primary cultured HLFs.

Among the four AdoR subtypes, the A_2B AdoR was expressed at the highest level, as determined by real-time RT-PCR. The rank order of AdoR mRNA levels was A_2B»A_2A>A₁, while A₃ receptor mRNA was undetectable. The effect of a stable analogue of adenosine, NECA, on the expression of the inflammatory cytokines was determined using a cytokine array and confirmed with ELISA. NECA increased the release of IL-6 by 16 folds, and this effect of NECA was attenuated by selective antagonists for the A_2B AdoR. Selective agonists for the A₁, A_2A, and A₃ AdoRs had no effect on IL-6 release. The differentiation of HLFs into myofibroblasts was determined using immunofluorescence staining of smooth muscle-alpha actin. NECA significantly increased the expression of smooth muscle-alpha actin, and this effect of NECA was abolished with the IL-6 neutralizing antibody.

These data suggest that NECA increases the release of IL-6 from HLFs via activation of the A_2B AdoRs, and IL-6 in turn induces HLF differentiation. Our findings suggest a novel mechanism whereby adenosine acts as a proinflammatory mediator in the lung.