Pulmonary function changes and increased Th-2 cytokine expression and nuclear factor kB activation in the lung after sensitization and allergen challenge in brown Norway rats

Background: Our purpose was to evaluate the expression of Th-1 and Th-2 related cytokine mRNA and nuclear factor (NF) kB in the lung tissue of ovalbumin (OA) sensitized brown Norway rats (BNR). We also evaluated the correlation between bronchial hyperreactivity (BHR) and eosinophils with cytokine mRNA expression. Methods: Eight BNR (weight range 250-350 g) were sensitized by inhaled OA (group I) with a 1-week interval between and then provoked with OA 1 week later. Pulmonary function tests (PFT) were performed at baseline and 24 h after acetylcholine challenge. Eight weight-matched normal BNR served as controls (group II). All animals were anesthetized, paralyzed with gallamine, and ventilated via tracheostomy. They were given varying doses of acetylcholine (25, 50, 75, 100 mu g/kg) injected through a jugular venous catheter. Five seconds after acetylcholine injections, PFTs were performed, including a maximal forced expiratory maneuver (MFEM), airway opening pressure (P-ao) at tidal breathing and total dynamic lung compliance (C-dyn). Bronchoalveolar lavage (BAL) was then performed with 20 ml normal saline divided into two doses. Thereafter, the lungs were removed and examined histologically. Total RNA was extracted from lung tissue samples and reverse-transcriptase polymerase chain reaction was performed using primers for mRNA of IL-4, IL-5, IL-10, interferon-gamma (IFNr) and beta-actine. Results: Group I OA treated rats had typical airway obstruction on PFTs and airway inflammation on histological examination. Ratios of IL-4, IL-5, IL-10 and inducible nitric oxide synthase (iNOS) mRNA levels to beta-actine as measured by densitometry were significantly lower in controls than in OA-sensitized rats. The IFNr mRNA to p-actin ratio was significantly reduced in OA-sensitized rats. Group I demonstrated a band shift when compared with group II in electromobility shift assay (EMSA) for NF-kappa B indicating increased activation of this transcription factor. Conclusion: Th-2 related cytokine mRNA was increased but Th-1 related cytokine mRNA was decreased in OA-sensitized BNR. An increased level of Th-2 related cytokine mRNA correlated with decreased airflow and inflammatory changes. These results demonstrate the value of the BNR model for studying allergic asthma at the molecular level. (C) 2000 Elsevier Science B.V. All rights reserved.