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

MR1-restricted MAIT cells display ligand discrimination and pathogen selectivity through distinct T cell receptor usage

Mucosal-associated invariant T (MAIT) cells express a semi-invariant T cell receptor (TCR) that detects microbial metabolites presented by the nonpolymorphic major histocompatibility complex (MHC)-like molecule MR1. The highly conserved nature of MR1 in conjunction with biased MAIT TCRα chain usage is widely thought to indicate limited ligand presentation and discrimination within a pattern-like recognition system. Here, we evaluated the TCR repertoire of MAIT cells responsive to three classes of microbes. Substantial diversity and heterogeneity were apparent across the functional MAIT cell repertoire as a whole, especially for TCRβ chain sequences. Moreover, different pathogen-specific responses were characterized by distinct TCR usage, both between and within individuals, suggesting that MAIT cell adaptation was a direct consequence of exposure to various exogenous MR1-restricted epitopes. In line with this interpretation, MAIT cell clones with distinct TCRs responded differentially to a riboflavin metabolite. These results suggest that MAIT cells can discriminate between pathogen-derived ligands in a clonotype-dependent manner, providing a basis for adaptive memory via recruitment of specific repertoires shaped by microbial exposure