Abstract: Abstract Objective:To investigate the effects of Bacillus Calmette-Guerin (BCG) on Th1/Th2 balance of human peripheral blood mononuclear cells (PBMC in asthmatic patients. Methods:PBMC were separated from 20 bronchial asthma patients and 10 non-atopic, age mathed healthy subjects as control. PBMC were cultured with BCG (100μg/ml) for 48h as postive group and PBMC were treated by saline as negative group. The mRNA expression of interleukin-4 (IL-4) and interferon-γ(IFN-γ) were measured by reverse transcription-polymerase chain reaction (RT-PCR) and the peripheral blood Th1/Th2 lymphocytes ratio by using three-color flow cytometry method. Results:The mRNA expression of IL-4 in asthmatics was significantly higher than that in healthy subjects while the mRNA expression of IFN-γwas lower significantly ( all P <0.05). And after BCG stimulation The IL-4mRNA expression decreased but IFN-γmRNA expression increased compared with untreated asthma group ( all P <0.05). The rate of Th1 and blood Th1/Th2 cells ratio were lower in asthma group compared with negative group ( all P <0.05) while the rate of Th2 was significantly higher than that in healthy gorup (P <0.05). After stimulation with BCG the rate of Th1 and Th1/Th2 ratio increased ( all P <0.05) , also the blood Th2 rate decreased compared with untreated asthma group (P <0.05). Conclusion:The Th2 immune response is stronger than Th1 immune response in bronchial asthma patients. BCG can retrieve the excursion of Th1/Th2 both on gene expression level and single-cell level.

Key words: Bronchial asthma, BCG, Th1/Th2, Flow cytometer, peripheral blood mononuclear cells.