Early T-cell development is affected in all Tg⁺ founder lines. Total immature progenitor thymocytes (DN) were gated on lineage-negative cells as described in “Materials and methods,” and classified from DN1 through DN4 according to the expression of CD44 and CD25 surface molecules. (A) Absolute DN counts from 6- to 12-week-old TgA (n = 8), TgH (n = 5), TgB (n = 9), and negative littermates (n = 15). ⁺P < .05. Error bars indicate SEM. (B) Appearance of a prominent population of CD44hi cells within DN1 and DN2 subpopulations in TgB line. Dot plots depict expression of CD44 versus CD25 on DN thymocytes from all 3 Tg⁺ lines versus Tg^– individual mice. The percentage of events corresponding to each quadrant is shown.