ATM deficiency alters thymic development.

(A) Thymocytes from four pairs of ATMWT and KO mice were analyzed by flow cytometry to enumerate cells in each CD4/CD8 subpopulation. (B) The DN3/DN4 ratio is elevated in ATMKO thymi. Representative CD44 and CD25 staining profiles of lineage negative ATMWT and KO DN cells and the calculated DN3/DN4 ratios are shown. Quantification of DN3/DN4 ratios measured in ATMWT and KO thymi (ATMWT vs KO p<0.025). (C) The DN/DP ratio is elevated in ATMKO thymi. Images show CD4/CD8 staining profiles and corresponding DN/DP ratios from representative ATMWT and KO thymi. Quantification of DN/DP ratios measured in ATMWT and KO thymi (ATMWT vs KO p<0.003). Data are mean (± SEM) of six separate experiments analyzing nine pairs of ATMWT and KO thymi. P values were calculated using Student’s paired 1-tailed t test.