Induction of T 'regulatory' cells by standardized house dust mite immunotherapy:: an increase in CD4+CD25+ interleukin-10+ T cells expressing peripheral tissue trafficking markers

Background Clinically effective subcutaneous allergen-specific immunotherapy (SIT) is associated with altered circulating T cell cytokine production and altered local cytokine responses with increased IL-10 following allergen challenge in target organs. Objective This study aimed to elucidate mechanisms for these T cell changes, by examining surface expression of markers for peripheral tissue trafficking on circulating cytokine-positive T cells following standardized house dust mite- (HDM-) SIT. Methods A randomized conventional HDM immunotherapy study was performed on a panel of 12 HDM-allergic subjects. Nine subjects received treatment with conventional HDM immunotherapy using a standardized extract and three subjects were treated by standard pharmacotherapy alone. Symptom and medication scores and allergen-induced cutaneous late-phase responses were assessed before and 9 months after institution of therapy. Before and at 3 and 9 months of SIT, peripheral blood mononuclear cells were cultured for 14 days with HDM extract and CD4(+) and CD8(+) T cell expression of CD62L, CD49d and CCR5 and production of IL-10, IFN-gamma and IL-4 were analysed by flow cytometry. Allergen-specific T cell proliferation was assessed by H-3-thymidine incorporation. Results At 9 months, all SIT-treated patients showed reduced symptom scores and late-phase cutaneous responses to HDM compared with baseline levels. The proportions of CD4(+) T cells which were IL-10(+) were increased (P<0.01), and the proportions of CD4(+) and CD8(+) T cells which were IL-4(+) decreased (P<0.05) compared with baseline. CD4(+) and CD8(+) T cell IFN-gamma production, expression of surface markers for peripheral tissue trafficking and allergen-specific proliferation remained unchanged during SIT treatment. However, increased proportions of CD4(+)CD62L(-), CD4(+)CD49d(hi), CD4(+)CCR5(+) T cells expressing IL-10 were detected at 9 months of SIT compared with baseline (P<0.05). IL-10 staining co-localized with CD4(+)CD25(+) T cells. Conclusion Clinically effective subcutaneous immunotherapy with a standardized HDM Dermatophagoides pteronyssinus preparation results in decreased numbers of IL-4(+) T cells and expansion of CD4(+)IL-10(+) T cells expressing a peripheral tissue trafficking phenotype. The co-localization of IL-10(+) staining to CD4(+)CD25(+) T cells is consistent with the induction of a T regulatory cell population by SIT.