Surface and intracellular phenotype of CLL SGs. PBMCs were incubated with goat F(ab’)² anti-human IgM coated beads and stained with antibodies for surface CD38 (A), CD25 (B), or CD5 (C) or for intracellular Ki67 (D) in the CLL SGs. CLL SGs were identified within the CD19⁺ population and the percentage of positive cells (CD38, CD25, or Ki67) or the MFI within each individual SG was determined. Analysis of CD38, CD25, and CD5 was performed using the FACS Calibur; Ki-67 used the FACS CANTO II.