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. 2013 Jun 27;38(6):1261-70.
doi: 10.1016/j.immuni.2013.06.003. Epub 2013 Jun 20.

Pathogen-specific Treg cells expand early during mycobacterium tuberculosis infection but are later eliminated in response to Interleukin-12

Shahin Shafiani  1 , Crystal Dinh, James M Ertelt, Albanus O Moguche, Imran Siddiqui, Kate S Smigiel, Pawan Sharma, Daniel J Campbell, Sing Sing Way, Kevin B Urdahl
Affiliations

Pathogen-specific Treg cells expand early during mycobacterium tuberculosis infection but are later eliminated in response to Interleukin-12

Shahin Shafiani et al. Immunity. .

Abstract

Thymically derived Foxp3⁺ regulatory T (Treg) cells have a propensity to recognize self-peptide:MHC complexes, but their ability to respond to epitope-defined foreign antigens during infectious challenge has not been demonstrated. Here we show that pulmonary infection with Mycobacterium tuberculosis (Mtb), but not Listeria monocytogenes (Lm), induced robust lymph node expansion of a highly activated population of pathogen-specific Treg cells from the pre-existing pool of thymically derived Treg cells. These antigen-specific Treg cells peaked in numbers 3 weeks after infection but subsequently underwent selective elimination driven, in part, by interleukin-12-induced intrinsic expression of the Th1-cell-promoting transcription factor T-bet. Thus, the initial Mtb-induced inflammatory response promotes pathogen-specific Treg cell proliferation, but these cells are actively culled later, probably to prevent suppression during later stages of infection. These findings have important implications for the prevention and treatment of tuberculosis and other chronic diseases in which antigen-specific Treg cells restrict immunity.

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Figures

Figure 1
Figure 1. Detection of ESAT-64–17-Specific Treg Cells in the pLNs of Mtb-Infected Mice
(A) Gating strategy used to identify CD3+CD4+ESAT-64–17-specific cells in the pLNs of B6 mice, 21 days after aerosol infection. PLNs from three Mtb-infected mice or all lymph nodes from an uninfected control mouse were pooled and enriched for ESAT-64–17-specific cells. (B) Binding of tetramer and expression of Foxp3 by CD4+ cells within pLN cells (day 21 after infection) after enrichment of tetramer-binding cells. The percentage of tetramer-binding cells expressing Foxp3 is shown. Histograms denote the amount of Foxp3 expression in tetramer-binding Treg cells (red), non-tetramer-binding Treg cells (blue), and Foxp3−CD4+ T cells (solid gray) in the pLN. Graph depicts mean fluorescent intensity (MFI) of Foxp3 within each of these three populations. Cumulative data from six independent experiments are shown. MFI values are normalized to those obtained for tetramer-binding Treg cells. Each solid square, triangle, or circle represents an experiment and the bars represent the mean of the six experiments performed. See also Figure S1.
Figure 2
Figure 2. ESAT-64–17-Specific Treg Cells Express an Activated Phenotype
(A) Expression of the indicated activation molecules by CD4+Foxp3+ cells that either bind (red) or do not bind (blue) the tetramer or by CD4+Foxp3− cells that either bind (black) or do not bind (solid gray) the tetramer in the pLN of Mtb-infected mice, 21 days after infection. Data are representative of three independent experiments. (B) ESAT-64–17-specific cells among CD4+ tetramer-enriched pLNs were gated for subsequent analysis of IFN-γ production (left). Middle panels depict direct ex vivo detection of intracellular IFN-γ by Foxp3-expressing or Foxp3− cells 21 days after infection. Staining with an isotype antibody of irrelevant specificity (clone MOPC-21) was used as negative control. Numbers represent the percentage of tetramer-binding Foxp3− or Foxp3+ cells producing IFN-γ in this representative experiment. Cumulative data from four independent experiments are also shown; each circle or triangle represents the percentage of IFN-γ within the indicated population. Each solid circle or triangle represents an experiment and the bars represent the mean of the four experiments performed. See also Figure S2.
Figure 3
Figure 3. ESAT-64–17-Specific Treg Cells Arise from Pre-existing Foxp3+ Precursors
(A) Gated on ESAT-64–17-specific CD4+ T cells (left), the expression of Foxp3 and Vβ6 is shown in the tetramer-enriched pLN of mice 21 days after infection. Numbers represent the percentage of cells within each quadrant. Cumulative data from three independent experiments are also shown; each symbol represents the percentage of Vβ6+ T cells within the indicated population. Each solid triangle or circle represents an experiment and the bars represent the mean of the three experiments performed. (B) Expression of Foxp3 and Helios is shown gated on non-tetramer-binding Foxp3+CD4+ T cells or the tetramer-binding Foxp3+ T cells from the enriched pLN on day 21 after infection. Numbers represent the percentage of cells in the quadrant. Cumulative data from three independent experiments show relative Helios expression by non-tetramer-binding Foxp3− cells, non-tetramer-binding Foxp3+ cells, and tetramer-binding Foxp3+ cells within the CD4-gated population of the same pLN. Because of variability in the MFI of Helios expression between individual experiments, values are normalized to those obtained for tetramer-binding Foxp3+ cells. Each solid square, triangle, or circle represents an experiment and the bars represent the mean of the three experiments performed. (C) CD45.2 and CD45.1 expression on CD4-gated T cells from tetramer-enriched pLN of T cell reconstituted Tcrb−/− Tcrd−/− mice on day 21 after infection. Foxp3-GFP expression and ESAT-64–17:I-Ab tetramer binding is shown for cells transferred as either Foxp3− precursors (CD45.2, blue gate) or Foxp3+ precursors (CD45.1, red gate). Numbers represent the percentage of cells within each quadrant. The experiment was performed twice and representative data are shown. See also Figure S3.
Figure 4
Figure 4. Expansion of ESAT-64–17-Specific Treg Cells Is Context Dependent
(A) Foxp3 expression and ESAT-64–17:I-Ab tetramer binding within CD4-gated tetramer-enriched pLN of Mtb-infected or Lm-ESAT-6-infected mice at day 21 or day 9 after infection, respectively. Pooled pLNs from each group were enriched for tetramer-binding cells, and the experiment was performed six times for Mtb and three times for Lm-ESAT-6. Numbers represent the percentage of tetramer-binding T cells that express Foxp3. (B) Cumulative data from six experiments with Mtb-infected and three experiments with Lm-ESAT-6-infected mice are shown. Each circle or triangle represents a time point. See also Figure S4.
Figure 5
Figure 5. Mtb-Specific Treg Cells Exhibit Early but Short-Lived Accumulation in the pLN
Mtb-infected mice were sacrificed at the indicated time points after infection, and cells from their lungs and tetramer-enriched pLNs were analyzed for tetramer binding and Foxp3 expression. Numbers in the quadrants represent the percentage of tetramer-binding cells that express Foxp3. Experiments were performed ten times at day 20 or 21, six times at day 32–35, and twice at each later time point.
Figure 6
Figure 6. Mtb-Specific Treg Cell Contraction Is Driven by IL-12-Induced T-bet Expression
(A) FACS plots represent column-enriched pLNs from Mtb-infected control wild-type (WT) B6 mice and mice deficient in IL-12p35 (Il12a−/−), IL-12p40 (Il12b−/−), and IFN-γ (Ifng−/−) analyzed for tetramer binding cells and Foxp3 expression. Mice were harvested at day 21 and 35 after infection with the exception of IFN-γ-deficient mice that were analyzed at day 32 because they had lost 20% of their body weight and appeared near death. Numbers in the quadrants represent the percentage of Foxp3+ cells within the tetramer-binding population. Experiments were performed four times for the WT and Il12b−/− mice, twice for Ifng−/− mice, and once for the Il12a−/− mice. Representative plots are shown. (B) Bar graphs represent absolute number of tetramer-binding Treg cells at the two time points in all the above groups. Mean ± SEM is shown for the WT and Il12b−/− groups. (C) Mtb CFUs in the lungs and pulmonary lymph nodes of the four groups of mice at the two time points are depicted (ND, not determined). Each solid circle, square, or triangle represents a mouse and the bar represents the mean of the group. (D) FACS plots represent column-enriched pLNs from Mtb-infected control Foxp3-IRES-Cre mice (FIC), and mice with conditional deficiency of T-bet expression in Foxp3-expressing Treg cells (Tbx21fl/fl:FIC), analyzed for tetramer-binding cells and Foxp3 expression. Mice were harvested at day 21 and 35 after infection. Numbers in the quadrants represent the percentage of Foxp3+ cells within the tetramer-binding population. Experiments were performed once for each time point. (E) Bar graphs represent absolute number of tetramer-binding Treg cells at the two time points in both groups. (F) Histograms denote the levels of T-bet expression in tetramer-binding Treg cells in either control FIC mice (red) or Tbx21fl/fl-FIC (purple) and CD44−Foxp3−CD4+ T cells (solid gray) in the pLN at day 21 after infection. See also Figure S6.
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