AID expression in human cord blood im/T1 B cells and fetal liver. AID mRNA expression in im/T1, T2, and MF B cell compartments from human cord blood (Fig. S5), and fetal liver samples were measured by quantitative RT-PCR. Unsorted cord blood cells (bulk) were compared to ensure that these B-cell compartments contained the majority of recovered AID message. Tonsil and Ramos cell lines served as positive controls. AID mRNA levels are shown as relative values to Igβ mRNA levels (mean ± SD, 4 independent measurements) in each sample. Each symbol represents an individual donor, subclone, or commercial source.