Flow cytometry of 2 unaffected individuals with MBL. Panels A-C show data on 2-1003; panels D-F, on 2-1006. (A) Analysis of whole blood stained with CD19 PerCP. The plot shows forward scatter versus CD19-isolating B cells. (B) Overall kappa-positive clone. (C) A subgate showing that the CD5 population is monoclonal (kappa light chain restricted). (D) The analysis of StemSep-enriched B cells (StemSep, Vancouver, BC, Canada). The plot shows CD19PerCP Cy5.5 versus CD5 PE Cy7. The top box shows a bright CD5 population, and the bottom box shows a dim CD5 population. (E) A subgate showing that the brighter CD5 population shown in panel D is monoclonal (kappa light chain restricted). (F) A subgate showing that the lower dim CD5 population present in panel D is polyclonal.