Aire affects the number of SP thymocytes. Thymocytes (3-week-old mice) generated by crossing (A) OT-II.Aire^+/− or (B) OT-I.Aire^+/− mice to nontransgenic Aire^+/− mice were analyzed by flow cytometry for expression of CD4, CD8, and Vα2 and enumerated for SP thymocytes expressing high levels of TCR, that is, (A) CD4⁺CD8⁻Vα2⁺ cells or (B) CD4⁻CD8⁺Vα2⁺ cells. Contour plots show a representative experiment. Histograms show the mean ± SEM for each group. n = number of mice pooled from several experiments. Significance relative to WT: *P ≤ .05; ***P ≤ .001.