CXCL13-expressing cells in human lymphoid neogenesis and normal secondary lymphoid tissue are CD11c⁺. (A-B) In situ hybridization for CXCL13 mRNA (red) in inflammatory lesions: (A) RA and (B) UC (insets, same fields with sense controls). Cells with CXCL13 mRNA are abundantly present in irregular lymphoid aggregates (arrowheads) and also scattered in areas with diffuse mononuclear cell infiltration (arrows). (C-E) Single exposures of multicolor immunofluorescence staining for CXCL13, CD11c, and CD20 (see keys) in inflammatory lesion or germinal centers of normal lymphoid tissue. CXCL13-expressing scattered CD11c⁺ cells (arrows) occur in small collections of CD20⁺ B cells in RA (C) lesion, and in germinal center of tonsil (D) or Peyer patch (E). Note that in the RA lesion the cells show different CXCL13 expression levels consistent with ongoing up-regulation, whereas in the germinal centers this level appears similar among the positive cells. Bars represent 200 μm (A-B) and 50 μm (C-E).