Immunocytochemical localization of NF-κB. Localization in human multiple myeloma cell lines (A), peripheral blood mononuclear cells (PBMCs) and CD138⁺ cells from healthy volunteers, and bone marrow CD138⁺ multiple myeloma cells from patient no. 1 (B). PBMCs were collected from the blood of a healthy subject by Ficoll-Paque density gradient centrifugation. CD138⁺ cells were enriched from bone marrow aspirates of a healthy volunteer and a multiple myeloma patient (patient no. 1), enriched by magnetic bead separation method, and immunostained for NF-κB (p65) as described in “Patients, materials, and methods.” Red stain indicates specific staining for NF-κB as indicated, whereas blue stain indicates the relative position of the nuclei in the corresponding view.