Allergen-specific immunotherapy (IT) has been effectively used for the treatment of asthma. Allergen specific IT induced immune tolerance with induction of TH2 cells anergy remain to be clarified. The aim of this study was to evaluate whether the mite allergen Dermatophagoides pteronyssinus (Dpt) specific IT serially decreased IL-4+/CD4+ (TH2) lymphocytes and induced apoptosis of TH2 lymphocytes in asthmatic children. Sixty Dpt-sensitive asthmatic children were randomly assigned to a received IT and an untreated group. Dermatophagoides pteronyssinus specific IT treated patients were examined at three time points: before IT, after 6 months of an increased dose phase and with maximum tolerated doses after 1 yr. Peripheral blood mononuclear cells (PBMC) were isolated and cultured for 48 h for cellular staining with CD4+, CD45RO cell phenotypes and interleukin (IL)-4 and interferon-gamma expression by fluorescence monoclonal antibodies. Apoptosis was measured using the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling (TUNEL) method. A simultaneous flow cytometric study using the same permeabilized cell was examined to determine whether apoptosis occurred preferentially in TH2 lymphocytes. The data demonstrated that Dpt specific IT decreased Dpt-specific IgE levels (p < 0.01) after 1 yr of treatment. In addition, decreased CD4+IL-4+ TH2 cells with increased CD4+IFN-gamma+ TH(1) cells were observed at 6 months and 1 yr after IT treatment (p < 0.05). At the same time, apoptosis of CD4+IL-4+ TH2 lymphocytes in the IT group had increased after 1 yr of treatment when compared with the results before treatment (p < 0.001) and after 6 months of treatment (p = 0.046). In addition, CD45RO cells apoptosis mainly occurred after 6 months of IT treatment and after 1-year period of IT treatment (p < 0.05). All of the data suggested that Dpt specific IT decreased Dpt specific IgE and CD4+IL-4+ TH2 lymphocytes with induction apoptosis of CD4+IL-4+ TH2 lymphocytes subsets serially.