Pathologic features of capillary damage in human digestive graft-versus-host disease. (A) Blood suffusion (arrow) around capillary loops (white broken lines) in the upper part of duodenal villi. Paraffin section with hematoxylineosin stain; original magnification, × 300. (B) High magnification of a capillary, with partial detachment of an endothelial cell (asterisk). Indirect immunoperoxydase with an antibody directed against CD31; original magnification, × 1200. (C) Ultrastructural aspect of close capillary sections in the lamina propria of a duodenal biopsy. 1: capillary section with intact endothelium and basal membrane; 2: capillary section with endothelial cytoplasm of irregular thickness around the capillary lumen, without basal membrane rupture; 3: capillary section with discontinuity in the basal membrane () and endothelial cytoplasmic cover; and 4: extravased red blood cells. Insert: higher magnification of basal membrane rupture.