Semiquantitative RT-PCR of RO-subdivided GC B cells. IgD⁻CD38⁺ GC B cells were cytometrically sorted based on their surface RO levels as defined in Figure 1A,B. RNA was immediately isolated and used in semiquantitative RT-PCR using β-actin to normalize RNA levels. Amplified targets included (A) CD45 isoforms highlighting RA and RO and (B). AID molecular weight markers are indicated to the left.