Expression levels of HLH, bHLH, and RAG-1 mRNAs on CD34⁺ FL-sorted populations. RNA was isolated from FACS-sorted human FL subpopulations from 3 separate donor pools and analyzed by RT-PCR. mRNA levels were compared with HPRT expression and expressed in arbitrary units (HPRT = 1). One representative experiment from 1 donor pool is shown. All assays were performed 4 to 6 times. Similar data were obtained with analyses of 2 other donor pools.