CD4⁺ CD25⁺ transforming growth factor-β-producing T cells are present in the lung in murine tuberculosis and may regulate the host inflammatory response

CD4⁺ CD25⁺ regulatory T cells produce the anti-inflammatory cytokines transforming growth factor (TGF)-β or interleukin (IL)-10. Regulatory T cells have been recognized to suppress autoimmunity and promote self-tolerance. These cells may also facilitate pathogen persistence by down-regulating the host defence response during infection with Mycobacterium tuberculosis. We evaluated TGF-β⁺ and IL-10⁺ lung CD4⁺ CD25⁺ T cells in a murine model of M. tuberculosis. BALB/c mice were infected with ~50 colony-forming units of M. tuberculosis H37Rv intratracheally. At serial times post-infection, lung cells were analysed for surface marker expression (CD3, CD4, CD25) and intracellular IL-10, TGF-β, and interferon (IFN)-γ production (following stimulation in vitro with anti-CD3 and anti-CD28 antibodies). CD4⁺ lung lymphocytes were also selected positively after lung digestion, and stimulated in vitro for 48 h with anti-CD3 and anti-CD28 antibodies in the absence and presence of anti-TGF-β antibody, anti-IL-10 antibody or rmTGF-β soluble receptor II/human Fc chimera (TGFβsrII). Supernatants were assayed for elicited IFN-γ and IL-2. Fluorescence activated cell sorter analyses showed that TGF-β- and IL-10-producing CD4⁺ CD25⁺ T cells are present in the lungs of infected mice. Neutralization of TGF-β and IL-10 each resulted in increases in elicited IFN-γ, with the greatest effect seen when TGFβsrII was used. Elicited IL-2 was not affected significantly by TGF-β neutralization. These results confirm the presence of CD4⁺ CD25⁺ TGF-β⁺ T cells in murine pulmonary tuberculosis, and support the possibility that TGF-β may contribute to down-regulation of the host response.