CD19 and infection: After sorting fluorescent cells and confirming infection by limiting-dilution PCR (LD-PCR)65 and p53 induction by flow cytometry (Supplementary Fig. 2a, c), we performed p53 pathway RT-PCR array analyses comparing infected cells, which were approximately 96% CD19+/B220+ B cells (Supplementary Fig. 2b), to uninfected B cells from infected animals.