Oxidative stress generated by intrinsic pollen NADPH oxidases is required for inducing allergic airway inflammation

Abstract

Rationale We have recently discovered that pollen-derived allergenic extracts directly induce oxidative stress in the lungs independent of adaptive immunity. Our goal was to identify the enzyme that is involved in this phenomenon and to delineate its role in allergic inflammation in the airways. Methods To determine the biochemical properties of pro-oxidant activity of pollen allergenic extracts we used NBT reduction test, cytochrome c assay, and in situ NBT reduction assay in non-denaturing polyacrylamide gels. We investigated the role of reactive oxygen species (ROS) generated by allergenic extracts in initiation of airway inflammation in murine asthma. Results We have discovered that all tested pollens important in allergic diseases contain NADPH oxidases. Upon exposure, these oxidases induce profound oxidative stress in the lungs independent of adaptive immunity. Avoidance or inhibition of this oxidative insult in experimental asthma significantly decreases pollen antigen-induced accumulation of eosinophils in the airways and peribronchial tissues, and formation of mucous cells in the airway epithelium. Conclusions We propose a two-signal hypothesis for initiation of pollen protein-induced allergic lung inflammation. In this model, oxidative stress induced by intrinsic pollen NADPH oxidases generates Signal 1, and presentation of pollen antigens to specific T-cells generates Signal 2. These signals act in concert to induce robust allergic airway inflammation.