Fig. 5. 6ß4 is expressed by endothelial cells in the adult mystacial pad. (A) Schematic representation of the vasculature associated with a whisker follicle (wf) in the adult mouse mystacial whisker pad. Small fur hairs (h) and a large whisker (w) are shown in dark gray. The epidermis (e), small hair follicles, and large whisker follicle are shown in light gray. The whisker follicle is surrounded by a vascular sinus (pink) which is enclosed by a dense collagen capsule (medium gray). Arteries, arterioles and capillary beds are red; veins and venules are blue; nerves are green; and piloerector muscles are brown (Fundin et al., 1997a; Fundin et al., 1997b; Rice et al., 1997). Dashed rectangles indicate areas comparable to sites in B,C, and in higher magnification in D-I. (B-I) Immunofluorescence staining of longitudinal sections of an adult whisker follicle. Adjacent sections were immunostained with anti-s100 (B,C: green) for Schwann cells on nerve axons. Double immunostaining with MEC 13.3 (B: red) labels PECAM-1 on the endothelium of all blood vessels. Double immunostaining with 346-11A (C: red) labels ß4 on the perineurium of nerves and endothelium of many blood vessels. Regions of B and C (dotted boxes) are shown at higher magnification (D,F,H) and (E,G,I) respectively. Arrows indicate nerves. Arrowheads indicate examples of ß4-positive vessels; dotted ovals indicate ß4-negative vessels. ß4 labeling is also present on basal keratinocytes (E, arrows) of the epidermis and hair follicles. Scale bars: 100 µm.