Microscopic morphology of BL vessels evaluated by staining with EVG reagent that is specific for elastin fibers in the external and internal elastic lamina of muscular arteries and the internal elastin lamina of large arterioles. Elastin fibers stain dark brown with EVG reagent. (A and B) Normal appearing patent vessels with continuous and regularly folded elastin laminas in tumor tissue from a mouse treated with formulation buffer. (C and D) Damaged vessels with fragmented or flattened elastin laminas associated with intravascular thrombosis in tumor tissue from a mouse bearing a regressing Burkitt's tumor treated with human rMig. (A and C), original magnification ×40; (B and D), original magnification ×63.