Immunocytochemical localization of gp-Fy in semithin cryosections of human thyroid (a and b), spleen (C through E), and lung (F and G). Antibody 6615 was used for labeling. (a) Fenestrated capillary endothelial cells (arrows) exhibited strong labeling, whereas epithelial cells (EP) were unlabeled. (b) When preimmune serum was used, no labeling was observed. (C) The capillaries and postcapillary venules of spleen were labeled. (D) The cuboidal cells of HEV showed strong labeling of both apical and basal plasma membrane domains. (E) When preimmune serum was used, no labeling was observed. (F ) The endothelial cells of the large venule (arrows) with multiple erythrocytes (V) exhibited strong labeling. Arrowheads show labeling of the squamous alveolar cell (pneumocyte type 1). (G) When preimmune serum was used, no labeling was observed. (Original magnification × 1,100.)