The AID protein is expressed in GC but not in post-GC-derived B-cell malignancies. Western blot analysis of AID expression in BL (top left panels), DLBCL (top right panels), and post-GC-derived B-CLL and MM samples (bottom panels). Both IgV mutated and unmutated cases were included in the B-CLL filter. The top right panel shows 2 pairs of isogenic BL cell lines representative of the group I/latency I and group III/latency III phenotype (see text for a detailed explanation); the B-cell lymphoma line BJAB serves as a negative control, because it does not express AID mRNA (L.P., unpublished results, 2003). In each membrane, equivalent amounts of total protein extracts from purified CBs were included; β-actin controls for loading.