Supplementary Figure 6: Localized IL-2 production by the DC population presenting antigen.

Il2^−/− thymic slices were overlaid with OT-II thymocytes followed by the addition of WT or Il2^−/− DCs loaded with 1mg/ml OVA protein. OT-II T_reg cell development was measured on d3. (a) Representative flow cytometry plots. (b) Quantification of the number of OT-II T_reg cells recovered per thymic slice. *p<0.001 by student’s t-test. Data representative of 3 independent experiments, n=8 slices per condition. (c) T_reg precursors (orange) interact with niche-defining APCs that bear agonist self-peptide (orange rectangles) and also supply IL2 (black dots). As precursors upregulate CD25 and differentiate into T_reg cells (blue) they limit IL2 availability from the APC, providing negative feedback and preventing future T_reg cell development within the niche. Shaded stars indicate cells in the surrounding tissue that are not part of the niche.