Human IL-10 Producing T Cells Specific for Mycobacterium tuberculosis.

IL−10 producing Mtb−specific CD4+ T cells can be detected in pulmonary TB patients with persistent anergy. Aim of the study was to define the spectrum of ex vivo frequencies of IL−10 producing Mtb−specific CD4+ and CD8+ T cells in adults. Peripheral blood mononuclear cells were collected from uninfected adults and subjects with latent tuberculosis infection or active tuberculosis. Monocyte−derived dendritic cells (DC) were infected overnight with Mtb (MOI=50:1) and incubated with different concentrations of positively selected autologous CD4+ and CD8+ T cells in an IL−10 ELISPOT assay. In all subjects we detected additional IL−10 producing cells with the addition of T cells to Mtb−infected DC, compared to Mtb−infected DC alone. We next focused on CD8+ T cells and asked if they represent the additional IL−10 producing cells. Autologous DC were left uninfected or infected with Mtb (MOI=20:1). After overnight incubation, positively selected CD8+ T cells were added and incubated overnight. Then, CD8+ T cells were positively selected from these cultures using magnetic beads, and RNA was isolated and subjected to RT−PCR. Relative quantitation of IL−10 RNA showed that CD8+ T cells were induced to produce IL−10 in response to Mtb−infected DC, suggesting that T cells are a source of the augmented IL−10 production previously seen in co−cultures of Mtb−infected DC with T cells. We next sought to isolate IL−10 producing Mtb−specific CD8+ T cells using a limiting dilution T cell cloning approach. T cells from wells exhibiting growth were analyzed by ELISPOT for their production of IFN−g and/or IL−10 in response to Mtb−infected autologous DC. In all donors, IFN−g producing CD8+ T cells were most frequently isolated. Most donors also had IL−10 producing CD8+ T cells, the majority of which also produced IFN−g. Finally, we confirmed that IL−10 has the potential to inhibit IFN−g CD4+ T cell responses to Mtb antigens.