Expression of AID-splicing variants in normal B cells. (A) Expression of various transcripts of AID in B cells of peripheral blood, tonsils, and spleens of healthy donors. An agarose gel image of RT-PCR products (top panel), the nested PCR (middle panel), and β-actin PCR loading control (bottom panel) is shown. (B) An agarose gel image of AID-nested RT-PCR on RNAs isolated from FACS sorted pure naive and memory B cells. To ensure the PCR sensitivity, cDNA inputs with 3 different dilutions (1:1, 1:4, and 1:16) were used in PCR amplification.