Abnormal T-cell development in IgH^P5ki mutant mice. (A) Decreased cellularity of the thymus in IgH^P5ki/+ and IgH^P5ki/P5ki mice. The average number of thymocytes (× 10⁶) was determined at 3, 6, and 12 weeks with at least 3 mice analyzed per genotype and time point. Error bars represent standard deviations of the mean. (B) Aberrant T lymphopoiesis in IgH^P5ki mutant mice. Total Thy1.2⁺ thymocytes of 3-week-old mice were examined for CD4 and CD8 expression and the Lin⁻Thy1.2⁺ DN thymocytes for CD44 and CD25 expression. (C) Reduction of DN and DP thymocytes in IgH^P5ki mutant mice at the age of 3 weeks. Absolute cell numbers (× 10⁶) are shown for the indicated mice (at least 4/genotype). (D) GFP expression of the IgH^P5ki allele (gray area) in the different thymocyte subsets. Black lines indicate the absence of GFP expression in wild-type thymocytes. (E) Variegated phenotype in a 6-week-old IgH^P5ki/+ mouse. The CD44/CD25 expression profile is shown for gated GFP⁻ and GFP⁺ cells of the Thy1.2⁺ DN thymocyte population.