Monocytoid B cells populate B henselae–induced granuloma and express the TCL1^– T-bet⁺ phenotype. Whereas in mycobacterial lymphadenitis only scattered CD20⁺ B cells surround the epithelioid granulomas (A), in a case of CSD suppurative granuloma numerous CD20⁺ B cells are found surrounding a central necrotic focus (*; B). (C) Double immunostaining for CD20 (red) and TCL1 (green) illustrates the distribution of TCL1⁺ cells in a reactive lymph node: nuclear expression of TCL1 is observed in a subset of CD20⁺ mantle B cells (Mn), in scattered CD20^– cells in the interfollicular area, and in germinal center B cells (Gc), whereas the majority of subcapsular monocytoid B cells (*) are negative (C). In CSD granuloma (D) the majority of CD20⁺ B cells associated with the granuloma are TCL1^–, whereas a mixture of double CD20⁺ TCL1⁺ and single CD20⁺ cells is found outside the granuloma. (E-F) Serial sections from a case of HIV lymphadenitis are stained for T-bet (E) and CD20 (F). Strong nuclear expression of T-bet is observed in clusters of CD20⁺ monocytoid B cells (*), whereas no reactivity is observed in other CD20⁺ follicular B cells (Gc indicates a germinal center). Numerous T-bet⁺ cells are associated with the CSD granuloma (G) and many of them coexpress CD20 (G inset). Immunoperoxidase technique for CD20 (A-B) and T-bet (E-G) counterstained with Meyer hematoxylin. Double immunofluorescence for CD20 (red), TCL1 (green), and T-bet (green) (C-D, G). Original magnifications, × 100 (A, E, F, G), × 200 (B-D), and × 600 (G inset).