Expression of components of the HLA class I APM in transformed plasma cells. Patients with MGUS are shown on the left; MM on the right. CD138⁺ cells were immunomagnetically purified from BMMCs and stained with DAPI (blue fluorescence) and with FITC-conjugated mAb (green fluorescence) to proteasome subunits δ (A-B) and LMP2 (C-D) or to the chaperone calnexin (E-F) and examined by epifluorescence microscopy.