CD4⁺CD25⁺FoxP3⁺ regulatory T cells suppress Mycobacterium tuberculosis immunity in patients with active disease

CD4⁺CD25⁺ regulatory T cells (Treg) play a central role in the prevention of autoimmunity and in the control of immune responses by down-regulating the function of effector CD4⁺ or CD8⁺ T cells. The role of Treg in Mycobacterium tuberculosis infection and persistence is inadequately documented. Therefore, the current study was designed to determine whether CD4⁺CD25⁺FoxP3⁺ regulatory T cells may modulate immunity against human tuberculosis (TB). Our results indicate that the number of CD4⁺CD25⁺FoxP3⁺ Treg increases in the blood or at the site of infection in active TB patients. The frequency of CD4⁺CD25⁺FoxP3⁺ Treg in pleural fluid inversely correlates with local MTB-specific immunity (p < 0.002). These CD4⁺CD25⁺FoxP3⁺ T lymphocytes isolated from the blood and pleural fluid are capable of suppressing MTB-specific IFN-γ and IL-10 production in TB patients. Therefore, CD4⁺CD25⁺FoxP3⁺ Treg expanded in TB patients suppress M. tuberculosis immunity and may therefore contribute to the pathogenesis of human TB.