BACKGROUND: Previous research has proved that nerve growth factor (NGF) participates in the onset of asthma by the induction of neurogenic inflammation.OBJECTIVE: To investigate the effect of interleukin-13 (IL-13) and interferon-γ(IFN-γ) on the expression of NGF mRNA in the splenic lymphocytes of bronchial asthma rats.DESIGN, TIME AND SETTING: The experiment, a completely randomized study based on cellular immunology, was performed in the Laboratory of Neurology in Chongqing Medical University and the Department of Clinical Pharmacy in College of Clinical Medicine, Chongqing Medical University (Chongqing, China) from January 2006 to April 2007.MATERIALS: Four adult male Wistar rats were used in this study. Rat IL-13, IFN-γprobe and the total RNA extraction kit were produced by Shanghai Sangon Biological Technology & Services Co., Ltd (China). The NGF ELISA kit was a product of Wuhan Boster Bioengineering Co., Ltd (China). A Du-70 automatic UV spectrophotometer was produced by Beckman Company (USA).METHODS: Rats were subjected to 1-mL intraperitoneal injections each containing 100 mg of ovalbumin, and were sensitized by using antigen solution, which was sensitized with 5×109 Bacillus pertussis and 100 mg aluminum hydroxide powder. Four rats were challenged with 1% ovalbumin using an ultrasonic nebulizer for 60 minutes to establish an asthmatic model. After rats were anesthetized, splenic lymphocytes were isolated and cultured in medium, which was supplemented with IL-13 or IFN-γ, for 0, 12, 24 or 48 hours. A parallel study was conducted with cultured splenic lymphocytes, which were divided into a control group, an IL-13 group and an IFN-γ group. Culture medium was added with different concentrations of IL-13 (10, 50, 100 μg/L) and IFN-γ (1, 10, 50 μg/L); 24 hours later, all samples were harvested.MAIN OUTCOME MEASURES: The expression levels of NGF mRNA were detected by reverse transcription-polymerase chain reaction.RESULTS: In the control group, the lymphocytes of the asthmatic model expressed NGF mRNA in a time-dependent manner. After lymphocytes were cultured with IL-13 at a final concentration of 50 μg/L for 12, 24 or 48 hours, expression of NGF mRNA was upregulated in a time-dependent manner to higher levels than the basal values at the same time points (P < 0.01). IL-13 upregulated the expression of NGF mRNA in a dose-dependent manner, and the NGF mRNA expression levels at middle and high concentrations of IL-3 were significantly higher than the values at a low concentration of IL-13 (P < 0.05). With increasing IFN-γconcentration, the expression of NGF mRNA was gradually downregulated. The low concentration group showed lower levels of NGF mRNA than the blank control group, while the middle and high concentration IFN-γgroups showed lower levels than the low concentration group (P < 0.05).CONCLUSION: In asthmatic rats, IL-13, a Th2 cytokine, upregulates the expression of NGF mRNA, while IFN-γ, a Th1 cytokine, downregulates NGF mRNA expression. The effects of both cytokines were time and dose dependent. Th1/Th2 cytokine immune imbalance may indirectly induce airway neurogenic inflammation by regulating NGF mRNA expression.