Bcl-2 onco-protein expression in HRS in a case of nodular sclerosis HD as detected by anti–bcl-2 MoAb on paraffin section. Virtually all HRS cells are immunostained with this antibody. The staining is mainly cytoplasmic and finely granular. Bcl-2–positive small lymphocytes are also seen and used as an inner control of the immunostaining (immunoperoxidase technique with nuclear counterstaining; original magnification × 400).