Figure 4.

IL-4 amplifies histamine-triggered H₂O₂ production in bronchial epithelial cells. (A) Submerged cultures of Cdk4/hTERT HBECs were treated with human IL-4 or IL-13 (10 ng/ml) for 2 days, and Duox gene expression levels were assessed by real-time RT-PCR. Data are from one representative experiment (n = 3). (B) Duox protein expression levels were induced in NCI-H292 or Cdk4/hTERT HBECs by IL-4 or IL-13 (10 ng/ml, 2 d). Data are from one representative experiment (n = 3). (C) Histamine stimulates H₂O₂ production in a dose-dependent manner (0–30 μM) in IL-4–induced Cdk4/hTERT HBECs (IL-4 treatment: 10 ng/ml, 2 d). Uninduced cells do not produce H₂O₂. H₂O₂ production was measured by homovanillic acid/horseradish peroxidase assay. Values are mean ± SEM. IL-4 induction: n = 4; no induction: n = 3. (D) Histamine 1 receptor agonist (100 μM) stimulates H₂O₂ production in IL-4–induced Cdk4/hTERT HBECs. Histamine 2,3,4 receptor (H1R–H4R) agonists had no effect. Noninduced cells were unresponsive to the agonists tested. (E) H1R antagonist inhibits histamine-stimulated (100 μM) H₂O₂ production in IL-4–induced Cdk4/hTERT HBECs in a dose-dependent manner. H2R antagonist had no effect. H₂O₂ production was measured by homovanillic acid/horseradish peroxidase assay. Values are mean ± SEM (n = 3). Ag, agonist; Ant, antagonist; unstim, unstimulated.