FL cells do not increase expression of surface Ig after incubation in vitro. Recovery of surface marker expression of FL samples in vitro (n = 9; 6 IgM⁺; 3 IgG⁺). FACS was used to determine expression (GeoMFI) of surface Ig for both (A) IgM-positive and (B) IgG-positive patients along with expression of CXCR4 (C and D) at zero time and at subsequent intervals up to 72 hours. Expression analysis of GeoMFI (CellQuest) was used to plot change of expression over time.