sIg light chain and IgD expression in CLL SGs. Light chain (either κ or λ) (A) or surface IgD expression (B) was analyzed within the CD19⁺ population on each SG in the FACS Calibur. Each line and symbol represents an individual CLL case. Values of light chain or IgD are represented as mean-fluorescence intensity on the y-axis. A nonparametric Mann-Whitney test was used to calculate the P value of the difference between SG1 and SG4. C shows the mean (± SEM) expression of Ig light chain or IgD in SG2, SG3, and SG4 relative to SG1 (normalized to 1 for each case).