The effect of Chinese herbal medicine, xiao-qing-long tang (XQLT), on allergen-induced bronchial inflammation in mite-sensitized mice

Background: There are detailed descriptions of the clinical experiences and prescriptions of asthma in traditional Chinese medicine. Xiao-qing-long tang (XQLT), or sho-seiryo-to by its Japanese name, is one of the Chinese herbal medicines used to treat bronchial asthma and allergic rhinitis for centuries. However, the therapeutic mechanisms of this medication are still far from clear. In this study, a house-dust-mite (Dermatophagoides pteronyssinus [Der p])sensitized murine model of asthma was used to evaluate the immunomodulatory effect of XQLT on the allergen-induced airway inflammation in asthma. Methods: Three different protocols were designed to evaluate the treatment and/or long-term prophylactic effect of XQLT in Der p-sensitized mice. XQLT extracts (1 gm/kg) were administered to sensitized mice 1 h before allergen challenge (AC) (group A), 24 h after AC (group B), and every other day six times before AC (group C), respectively. Cellular infiltration and T-cell subsets in the bronchoalveolar lavage fluid (BALF) of allergen-challenged mice were analyzed. Intrapulmonary lymphocytes were also isolated to evaluate their response to allergen stimulation. Results: When XQLT was administered to the sensitized mice before AC (groups A and C), it suppressed airway inflammation by decreasing the number of total cells and eosinophil infiltration in the BALF, and downregulated the allergen- or mitogen-induced intrapulmonary lymphocyte response of sensitized mice as compared to those of controls. This immunomodulatory effect of XQLT may be exerted through the regulation of T-cell subsets by elevation or activation of the CD8⁺ and double-negative T-cell population in the lung. However, the administration of XQLT to sensitized mice 24 h after AC (group B) did not have the same inhibitory effect on the airway inflammation as XQLT given before AC. Conclusions: The administration of XQLT before AC has the immunomodulatory effect of reducing bronchial inflammation in the allergen-sensitized mice.