AID-splicing variants are singly expressed in individual tonsillar B cells. Purified human tonsillar B cells were limiting diluted into 96-well PCR plates at the densities of 200 cells/well and 1000 cells/well (depicted in top panels). The wells filled with various colors indicate where AID was positively detected, and the color codes show the identities of the AID PCR products. (Bottom panel) DNA gel image showing the amplified AID variants from those PCR-positive wells.