Developmentally regulated levels of AID expression in murine B-cell compartments. Levels of AID mRNA in pro-/pre-, im/T1, MF and GC B cell compartments from BM or spleen of BL/6, CD154−/− and AID−/− mice, and subcloned AMuLV-transformed cell lines, were determined by a quantitative RT-PCR. AID mRNA levels are shown as relative values to Igβ mRNA levels (mean ± SD) in each sample. B cell subsets (●, n = 3–6); AMuLV-transformed cell lines: S/B6 (●), C12 (), PD31 (▲), KG7 (▼;), 63-12 (), and 220-8 (◆), n = 2. Statistical significance was determined using Student’s t test