Expression of Th‐2 cytokines interleukin‐4 and −5 and of Th‐1 cytokine interferon‐γ in ovalbumin‐exposed sensitized Brown‐Norway rats

We determined the expression of Th-2 type cytokines, interleukin-4 (IL-4) and IL-5, and of the Th-1 type cytokine, interferon-gamma (IFN-gamma), in the Brown-Norway rat. Rats were intraperitoneally sensitized with ovalbumin and 21 days later were either exposed to ovalbumin or saline aerosol. The value -log PC300 (PC300 = concentration of acetylcholine needed to increase baseline lung resistance by 300%) was 2.49 +/- 0.15 in sensitized, exposed rats, was higher than in sensitized, saline-exposed or naive rats (1.54 +/- 0.27 and 1.63 +/- 0.06 respectively, P < 0.05). There was a significant increase in eosinophils in bronchoalveolar lavage fluid and in airway submucosal airway tissues in the sensitized exposed group. Reverse-transcriptase polymerase chain reaction was performed on total lung RNA using primers for IL-4, IL-5, IFN-gamma and beta-actin. IL-4 and IL-5 mRNA levels in control and sensitized saline-exposed rats were not detectable, but increased levels were found in sensitized and ovalbumin-exposed rats with levels of 0.25 +/- 0.01 and 0.98 +/- 0.02% of beta-actin mRNA as assessed by densitometric measurements. Expression of IFN-gamma mRNA was significantly reduced in sensitized and ovalbumin-exposed rats. As in asthmatic airways, there is an increased expression of Th-2 cytokines, IL-4 and IL-5, together with a reduction in the Th-1 cytokine, IFN-gamma, thus supporting a role for Th-2 cytokines in allergic eosinophilic inflammation.