Preferential circulation of p-Ts in early fetuses. (A) Frequency of p-Ts and p-Bs in the IL-7R⁺ population from the FL and FB of various days of gestation. Single cells of the Lin^–c-kit⁺IL-7R⁺ population from FB between 10.5- to 14-dpc fetuses were cultured under MLP assay conditions. Numbers of p-Ts and p-Bs detected among 100 IL-7R⁺ cells at different days of gestation were plotted against the gestational age. Data for 12-dpc and 13-dpc IL-7R⁺ cells are from the experiments shown in Figure 2. Frequency of p-T (▴) and p-B (▵) in FB of athymic nude mice are also shown. (B) Total numbers of p-Ts and p-Bs in the IL-7R⁺ population from the FL and FB of various days of gestation. In calculating the number of progenitors per FB, the numbers and proportions of IL-7R⁺ cells in a fetus at 10.5- to 14-dpc shown in Figure 1 were used. For comparison, the numbers of p-Ts and p-Bs in the IL-7R⁺ population of FL at the same gestational ages are shown. Total numbers of p-T (▴) and p-B (▵) in FB of nude mice are also shown.