Claudin 1 in DC1 lineage regulates central tolerance. (A) Frequency of Tregs and their precursors within CD4⁺ T cells isolated from thymi of I-ab^fl/fl (control; solid circle) and XCR1^iCreI-ab^fl/fl (empty circle) mice related to Fig. S4 C (mean ± SEM, n = 13–14 mice from four independent experiments). (B) Frequency of SP Tregs within CD4⁺ T cells from I-ab^fl/fl (control; solid circle) and XCR1^iCreI-ab^fl/fl (empty circle) mice, related to S4E (mean ± SEM, n = 7 mice from two independent experiments). (C) Schematic of the generated Defa6^iCreR26^TdT-OVA model. (D) Schematic of donors and recipient genotypes used for competitive BM chimera experiments, which assess the role of Claudin 1 in Treg selection and clonal deletion. Mouse models used are marked by the letters (a–f). Ratio for the preparation of BM mixtures is indicated. (E) Symbols used across Figs. 6 and 7 and their supplements for the negative control samples (a+b+d→f, solid black circle), positive control samples (a+b+d→e, empty black circle), and test samples (a+b+c→e, violet circle) are shown. (F) Frequency of OTII Tregs and their CD25⁺ and Foxp3⁺ precursors within all OTII cells from thymi of competitive BM chimeras described in Fig. 6, D and E (mean ± SEM, n = 5–10 mice from two independent experiments). (G) Frequency of conventional OTII cells within all live cells from thymi of competitive BM chimeras described in Fig. 6, D and E (mean ± SEM, n = 5–10 mice from two independent experiments). (H) Frequency of OTII Tregs within OTII cells from skin-draining lymph nodes of competitive BM chimeras described in Fig. 6, D and E (mean ± SEM, n = 7–14 mice from three independent experiments). (I) Frequency of conventional OTII cells within live cells from skin-draining lymph nodes of competitive BM chimeras described in Fig. 6, D and E (mean ± SEM, n = 7–14 mice from three independent experiments). (J and K) Frequency of polyclonal Tregs from polyclonal CD4⁺ T cells (J) and newly generated (CD73⁻) and recirculating Tregs (CD73⁺) from polyclonal Tregs (K) gated as in Fig. S4 K from thymi of competitive BM chimeras described in Fig. 6, D and E (mean ± SEM, n = 5–10 mice from two independent experiments). Statistical analysis in A, B, F, and H was performed using unpaired, two-tailed Student’s t test and in G, I, J, and K using one-way ANOVA with Tukey’s multiple comparisons, *P ≤ 0.05, **P ≤ 0.01, ****P < 0.0001, ns = not significant. All mice were bred on the B6 background. Littermates were used as controls.