FLLCs are nonproliferative cells. (A) Distribution of the t(14;18)^pos cells within proliferative CD20^posCD10^pos CXCR4^posHoechst^pos centroblasts vs CD20^posCD10^posCXCR4^negHoechst^neg nonproliferative centrocytes cell sorted from a t(14;18)^hi RLN7 sample. Genomic DNA from each GC subsets was tested using a 2-step fluctuation nested PCR assay consisting of 16 replicates. BCL2/IGH translocations were sequenced. Multiple size bands revealed oligoclonality. (B) CFSE-labeled CD20^pos purified B cells from RLN4 were stimulated for 4 days. Highly proliferative viable CFSE^loDAPI^neg and nonproliferative viable CFSE^hiDAPI^neg B cells were then sorted before quantification of t(14;18) by qPCR. Standard curves were generated from cloned BCL2/IGH (red) and GAPDH (green) PCR products, and it was demonstrated that detection of the BCL2/IGH transcript from the CFSE^hi population was above the CFSE^lo cell population, where it remained below the quantification threshold of 1/25 000 cells. NQ, not quantifiable.