Immunocytochemical localization of gp-Fy in semithin cryosections of human kidney cortex (a and b), outer medulla (c), and inner medulla (d and e). Antibody 6615 was used for labeling except in (f ). (a) Capillary endothelial cells within the glomerulus (arrows) and peritubular capillaries exhibited strong labeling. (Original magnification × 500.) (b) Cortical peritubular capillaries were labeled, while proximal and distal tubules were unlabeled. (Original magnification × 1,100.) (c) In outer medulla, strong labeling of vascular structures was seen (arrows), whereas multiple thin walled structures (descending thin limbs) were unlabeled (arrowheads). (d) In the inner medulla, strong labeling of vascular structures was seen (arrows), whereas multiple thin walled structures (descending and ascending thin limbs) were unlabeled (arrowheads). Collecting ducts exhibited strong labeling in the apical and basolateral plasma membrane domains (small arrows). (Original magnification × 1,100.) (e) When preimmune serum was used, no labeling was observed. (f ) Paraffin section of human kidney inner medulla labeled with anti-Fy6. There was faint labeling seen in some thin structures, presumably capillaries, whereas collecting ducts (arrows) exhibited strong labeling. (Original magnification × 240.) (Inset D) Paraffin section of human kidney labeled with immunopurified antibody 6615. The abundant labeling of capillary endothelium (arrow) confirmed the specificity of antibody 6615.