(A) AIDS-related KSHV⁺ PEL (patient no. 5). The majority of tumor cells show strong cytoplasmic and membrane staining for B-B4 antibody that recognizes the plasma cell-specific CD138/syndecan-1 antigen. Cytospin preparation, APAAP immunostaining, hematoxylin counterstain. (Original magnification × 400.) (B) AIDS-related KSHV⁺ PEL (patient no. 5). High power photograph showing pleomorphic tumor cells with intense membrane staining for B-B4 antibody. Cytospin preparation, APAAP immunostaining, hematoxylin counterstain. (Original magnification × 1,000 oil immersion.) (C) AIDS-related KSHV⁺ PEL-derived cell line (HBL-6). Cultured cells show a dominant membrane staining for B-B4 antibody. Cytospin preparation, APAAP immunostaining, hematoxylin counterstain. (Original magnification × 320.)