Expansion and function of Foxp3-expressing T regulatory cells during tuberculosis

Mycobacterium tuberculosis ( Mtb) frequently establishes persistent infections that may be facilitated by mechanisms that dampen immunity. T regulatory ( T reg) cells, a subset of CD4(+) T cells that are essential for preventing autoimmunity, can also suppress antimicrobial immune responses. We use Foxp3-GFP mice to track the activity of T reg cells after aerosol infection with Mtb. We report that during tuberculosis, T reg cells proliferate in the pulmonary lymph nodes ( pLNs), change their cell surface phenotype, and accumulate in the pLNs and lung at a rate parallel to the accumulation of effector T cells. In the Mtb -infected lung, T reg cells accumulate in high numbers in all sites where CD4(+) T cells are found, including perivascular/ peribronchiolar regions and within lymphoid aggregates of granulomas. To determine the role of T reg cells in the immune response to tuberculosis, we generated mixed bone marrow chimeric mice in which all cells capable of expressing Foxp3 expressed Thy1.1. When T reg cells were depleted by administration of anti-Thy1.1 before aerosol infection with Mtb, we observed similar to 1 log less of colony-forming units of Mtb in the lungs. Thus, after aerosol infection, T reg cells proliferate and accumulate at sites of infection, and have the capacity to suppress immune responses that contribute to the control of Mtb.