Abstract: Objective To identify whether CD4+CD25+FoxP3+regulatory T cells(Treg) are expanded in patients with active pulmonary tuberculosis(TB) and to characterize Treg functions in the modulation of antigen-specific responses. Methods The frequency and the immune function of circulating regulatory T cells were compared in the patients with active pulmonary TB and heathy control subjects using flow cytometry analysis,proliferation assays and determination of cytokines. Results The percentage of CD4+CD25+FoxP3+regulatory T cells within the total CD4 CD4+ population was significantly increased in the peripheral blood in active pulmonary TB patients than that in heathy control subjects(p<0.01).The peripheral blood mononuclear cells(PBMCs) of pulmonary TB patient had significantly higher cellular proliferation and IFN-γ production in response to both Bacille Calmette Guerin(BCG) and early secretory antigenic target-6(ESAT-6) compared to PBMCs from healthy donors(all p<0.05).In active pulmonary TB patients, the peripheral blood CD4- T cells had higher BCG-induced IFN-γ and IL-10 production (1289.62±519.01 and 1045.40±534.12, respectively) compared to PBMCs(624.50±261.13 and 377.00±249.56, respectively)(all p<0.05). These CD4+CD25+FoxP3+regulatory T lymphocytes are capable of suppressing IFN-γ and IL-10 production in response to both BCG and ESAT-6 in peripheral blood CD4+CD25- cell from TB patients. Conclusions CD4+CD25+FoxP3+ Regulatory T cells expanded in patients with active pulmonary TB may therefore contribute to the pathogensis of human TB by suppressing specific Mycobacterium tuberculosis cellular immune responses.

Key words: CD4+CD25+FoxP3+regulatory T cells, mycobacterium tuberculosis, immunity, pulmonary tuberculosis