Figure 2. Triple-immunoperoxidase-labeled frozen section showing the relationship among mast cells, blood vessels, and nerves. Peripheral nerves stained with antibodies to neurofilament protein are brown, while the CD31 (PECAM-1) adhesion molecule on the luminal surface of the blood vessel is stained pink. Tryptase in mast cells is stained black. Several mast cells are present in the section. Two of these (indicated by arrows) are juxtaposed between nerves and blood vessels. Original magnification X400. Scale bar represents 20 µm.