Figure 3.

Type B IELps have a thymus-emigrating phenotype in early life. (A) Flow cytometry for PD-1 and Tbx21^GFP within CD25⁻CD1dtet⁻TCRβ⁺CD5⁺ DN thymocytes for the identification of type A (PD-1⁺Tbx21^GFP−; red) and type B (PD-1⁻Tbx21^GFP+; blue) IELps in 15-d-old Tbx21^GFP mice. (B and C) Thymic H-2K^b+ (mature) CD4SP cells and type A (PD-1⁺; red) or type B (PD-1⁻; blue) IELps of 15-d-old Klf2^GFP mice were analyzed for GFP and S1PR1 expression by flow cytometry (B), and the frequency of Klf2^GFP+S1PR1⁺ cells was summarized (n = 3; C). (D–G) Type A (PD-1⁺Tbx21^GFP−; red) and type B (PD-1⁻Tbx21^GFP+; blue) IELps in 15- (n = 4–7), 18- (n = 8 or 9), or 21- (n = 3–5) day-old or adult (n = 3–5) Tbx21^GFP mice were analyzed for surface expression of CD103 and α4β7. The expression levels in 15-d-old versus adult animals are shown as histograms (D and F), while the bar graphs depict the frequencies of CD103⁺ type B IELps (E) or α4β7⁺ type A and type B IELps (G). Data in C, E, and G are pooled from at least three independent experiments and show the mean ± SD. *P < 0.05, **P < 0.01, and ***P < 0.001 (ANOVA with Bonferroni post-test in C, E, and G). Tp., type.