BACKGROUND:Mesenchymal stem cel s have an immunoregulatory capacity to suppress the airway inflammation of asthmatic mice, but the mechanism remains unclear. Our preliminary studies indicated that mesenchymal stem cel s can upregulate the CD4+CD25+regulatory T cel s (Treg) of the asthmatic mice. OBJECTIVE:To study the effect of mesenchymal stem cel s on the airway inflammation in asthmatic BALB/c mice depleted of CD4+CD25+Treg. METHODS:Forty BALB/c mice were randomly divided into five groups:normal control group (group A), asthmatic group (group B), asthmatic group depleted of CD4+CD25+Treg (group C), mesenchymal stem cel s group (group D), and asthmatic group depleted of CD4+CD25+Treg and administrated with mesenchymal stem cel s (group E). Except group A, mice in the other groups were sensitized and chal enged by ovalbumin to establish asthma models. In group C and group E, each mouse was treated with anti-CD25+monoclonal antibody to deplete CD4+CD25+Treg. In group D and group E, mice were intravenously administered with 0.2 mL mesenchymal stem cel s 1×109/L) at 10 days after sensitization. At 24 hours after the final activation, the number of CD4+CD25+Treg in the peripheral blood was detected by flow cytometry. The total cel number of inflammatory cel s in the bronchoalveolar lavage fluid, and the number of eosinophils, lymphocytes and neutrophils were counted to analyze the degree of inflammation of the airway together with pathological observation. RESULTS AND CONCLUSION:(1) The proportion of CD4+CD25+Treg in peripheral lymphocytes was ranged as fol ows:group B