CCL21 protein is expressed in HEVs and is also associated with extracellular fibrils in normal human lymphoid tissues. Single-color separations in black and white and color merges of multicolor immunofluorescence staining for CCL21, PNAd (MECA-79), and fibronectin (see keys on panel). CCL21 immunostaining is seen in HEVs (arrows) in (A) normal mesenteric lymph node, (B) tonsil, and (C) PP. The strongest CCL21 staining in HEVs (arrows) is seen at the basal side, associated with the reticular network around HEVs, whereas MECA-79 staining in HEVs is strongest at the luminal face. CCL21 is also associated with the reticular network outside HEVs (arrowheads) at the sites of other vascular structures resembling lymphatics and elsewhere in the stroma.