Bone marrow biopsy in HCL stained with anti-CD20 monoclonal antibody. This figure (HCL patient bone marrow biopsy) was stained with anti-CD20 monoclonal antibody (Dako North America) and detected using a horseradish peroxidase–conjugated mixed secondary detection system (LSAB; Dako North America). The image was obtained using an UPlanFL 20× Olympus objective. The image was collected using an MTI 3 CCD camera (DAGE-MTI Inc) with PAX-it 2.0 acquisition software (MIS).