BSAP expression in reactive lymphoid tissues and lymphomas. (A) BSAP transcripts are strongly expressed in lymphoid cells of the germinal center and the mantle zone but are largely absent from interfollicular cells (tonsil, in situ hybridization). (B) BSAP is not found in CD3⁺ lymphocytes but present in mantle zone and germinal center cells (tonsil, immunohistological detection of CD3 [peroxidase, brown color] and BSAP [APAAP, red color]). (C through E) BSAP expression in Piringer’s lymphadenitis. (C) In addition to a secondary follicle, monocytoid B cells (arrow) and some interfollicular blasts are labeled whereas most interfollicular lymphoid cells are negative (APAAP-staining). (D and E) Higher magnifications of (C); these show labeled germinal center and mantle zone cells (D) and monocytoid B cells (E). (F) The neoplastic cells of an intestinal Burkitt lymphoma express BSAP protein (APAAP-staining). (G) The CD30⁺ tumor cells of a systemic anaplastic large cell of T-cell type do not express BSAP (immunohistological detection of CD30 [peroxidase, brown color] and BSAP [APAAP, red color]). (H) BSAP expression in this case is restricted to CD20⁺ reactive cells whereas the neoplastic cells are not labeled (immunohistological detection of CD20 [peroxidase, brown color] and BSAP [APAAP, red color]). HRS cells of cHD display BSAP transcripts (I; in situ hybridization) and BSAP protein (J, APAAP staining).(K) Allocation of the BSAP expression to HRS cells is confirmed by the coexpression of CD30 (immunohistological detection of CD30 [peroxidase, brown color] and BSAP [APAAP, red color]).