Figure 7.

AID expression in immature, bone marrow B lymphocytes. (A) AID expression determined by flow cytometry from bone marrow B220^lowIgM⁻ pro–/pre–B (population 1), transitional B220^lowIgM⁺ (population 2), and recirculating B220^highIgM⁺ (population 3) B lymphocytes obtained from AID-GFP (left histograms) or AID-Cre-YFP (right histograms) mice. All immature B cells were also CD93⁺ (not depicted). Antibodies were IgM-APC, B220-PercP-Cy5.5, CD93-biotin/Streptavidin-PE, and To-pro-3. (B) Real-time PCR analysis of AID transcripts in pro–, pre–, transitional, mature, and PP B lymphocytes cell sorted from wild-type mice. For comparative purposes, cDNA synthesized from GL7⁺CD95^high GC B cells was serially diluted, as indicated below each column. cDNA was amplified using PCR primers annealing to AID exons 2 and 3. All B cell populations were sorted to >95% purity before RNA extraction and cDNA synthesis. Vertical bars represent the standard deviation of three independent experiments. (C) Bone marrow cells from AID-Cre-YFP mice were infected with Ab-MLV in vitro. The appearance of YFP⁺ cells was monitored in the infected cultures as a function of time (panels 1–4; only days 1 and 7 after infection are shown). The images are representative of three independent experiments. Panel 5 represents bone marrow B220⁺ cells isolated from AID-Cre-YFP mice and cultured for 7 d with IL-7 and in the presence of S17 cells. The following antibodies were used: CD43-PE, IgM-APC, B220-PercP-Cy5.5, and DAPI. Bar graph depicts the relative AID expression assessed by real-time PCR in Ab-MLV cultures.