CXCL13-expressing cells in human lymphoid neogenesis and germinal centers of normal or aberrant human lymphoid tissue show macrophage phenotype. Multicolor immunofluorescence staining for CXCL13 and various markers (merged color separations; see keys). (A-B) All CD11c⁺ cells in follicles of UC lesion (A) and tonsil (B) with extensive germinal centers coexpress cytoplasmic CD68⁺ (right inset, enlarged cellular details). These cells appear red with yellow or green periphery because CD68 is intracellular, whereas CD11c is a surface marker. Outside of the CD20⁺ B-cell follicle are numerous purely red (CD68⁺CD11c^–) macrophages in UC (A), whereas scattered red macrophages and abundant purely green dendritic cells (CD11c⁺CD68^–) are seen in the extrafollicular area of tonsil (left inset, enlarged cellular details). Macrophages sometimes appear yellowish because of weak coexpression of CD11c. (C) CXCL13 is localized to the cytoplasm of CD11c⁺ cells in tonsillar germinal center; comparable field from section adjacent to panel B. (D) CXCL13-expressing scattered cells in dense collections of T cells (CD3⁺) are CD68⁺ (arrows) in UC lesion. Bars represent 100 μm (A-C) and 50 μm (D).