Relationship between B-cell lymphomas in individual infected by HIV and B-cell differentiation stage related to the different zones of the lymphoid follicle. B-cell lymphomas putatively develop from the malignant transformation of B cells at various stages of differentiation. The definition of cell of origin (COO) starts from the assumption that B-cell lymphomas are frozen at a given B-cell differentiation stage associated with different zones of the lymphoid follicle. The figure shows a lymphoid follicle of a reactive lymph node stained by multiplex immunostaing. In the different zones of the follicle B lymphocytes express CD20 (brown). In the germinal center (GC), B lymphocytes also express Ki67 (gray), whereas outside the marginal zone of the follicle, T lymphocytes express CD3. CD3-positive cells are also scattered in the mantle zone and in the GC. Regarding lymphomas, HL corresponds to GC B cells, and BL tumor cells correspond to centroblasts. GC B cell–like DLBCL corresponds to B cells that are arrested at various stages of the GC transits and the activated B cell-like DLBCL seems to derive from GC B cells evolving to plasma cell differentiation. PBL and PEL seem to derive from GC B cells resembling plasmablasts. Marginal zone lymphoma (MZL) corresponds to marginal zone B cells. Original magnification, ×200. Images were taken using a Nikon Eclipse 80i microscope with a Plan Fluor 20×/0.75 objective and Nikon digital sight DS-Fi1 camera equipped with control unit-DS-L2. Images were processed using Adobe Photoshop CS2 V9.0.