A comparative study of the effects of BCG-polysaccharide--nucleic acid(BCG--PSN) and dexamesone on the expressions of IL--4 and IFN--#gamma# mRNA

The effects of BCG-polysaccharide-nucleie acid (BCG-PSN) and dexamesone on the expression of IL-4 and IFN-γ mRNA were investigated in the molecular level to explore the possible mechanism for their therapeutic action on asthma in rats, in which 32 SD rats were used for study and were randomly divided into saline control group, BCG-PSN group dexamesone group and asthma group, 8 rats in each groups, and the rat model of asthmatic inflammation was induced by sensitization with 10% ovalbumin(OVA) and alum AL(OH)3, each with 1 ml, intraperitoneally injected in 1, 7, and 14 days respectively. Two weeks after the establishment of rat asthmatic model, BCG-PSN(5 mg/kg per day), dexamesone(5 mg/kg per day) and saline were administered intraperitoneally for 7 consecutive days into the BCG-PSN and dexamethone-treated groups and the saline control group of 32 SD rats, respectively, while the saline control group of rats was received with saline injection and saline aerosol 24 hours later after the last provocation. Thereafter, brochioalveolar lavage fluids (BALF) and the lung tissues were to be taken from rats under anaesthesia. The total RNA was extracted from lung tissues, and the expressions of IL-4 and IFN-γ mRNA were determined by reverse transcriptase-polymerase chain reaction(RT-PCR) using primers for IL-4, IFN-γ and β-actin. Experimental results showed that in the BCG-PSN treated group of rats, the allergic symptoms and the inflammatory infiltration in the musosa of bronchus and lung were hardly observed, and most importantly, it was found that the expression of IFN-γ mRNA was significantly increased with a decreased expression of the IL-4 mRNA, as demonstrated by RT-PCR. In the dexamesone treated group of rats, the allergic symptom were not so obvious, and the inflammatory infiltrations both in BALF and lung tissues were rarely observed. However, the expression of IL-4 mRNA in this group was significantly decreased in comparison with those of the asthma and the saline control groups, while the change in the expression of IFN-γ was not obvious. Yet, in the asthma group, the allergic symptoms were observed and rales could be demonstrated in 4 rats, and there was an obvious increase of the inflammatory cell(such as EOS) both in BALF and lung tissues. In this group, the expression of IFN-γ mRNA was decreased and that of IL-4 mRNA was increased in comparison with those of the 3 other groups. It is concluded from the results of this study that BCG-PSN can significantly increase the expression of IFN-γ mRNA with a depressed expression of IL-4 mRNA by dual-way modulation in the asthma model of rats, so as to reverse the imbalance of Thl/Th2 responses, thus it may become a potential therapeutic agent for the immunotherapy of asthma. Dexamesone can significantly decrease the expression of IL-4 mRNA, but it has little effect on the expression of IFN-γ mRNA.