T-cell and thymocyte subsets. (A,B) Lymph nodes, spleen, and (C) thymus from wild-type and p38α^Y323F mice were homogenized. Cells were counted, then stained for CD4, CD8, and B220 (n = 10; bars indicate mean ± SEM). (C) Double-negative thymocytes were stained for CD44 and CD25 and the number of cells in different developmental stages are shown (n = 4; bars indicate mean ± SEM; P value was calculated with the Student t test). DN1 = CD44⁺CD25⁻, DN2 = CD44⁺CD25⁺, DN3 = CD44⁻CD25⁺, DN4 = CD44⁻CD25⁻.