Binding of HCII to carotid arterial sections in vitro. Frozen sections were incubated for 1 hour at room temperature with 20 μg/mL rHCII^WT (A), rHCII^K173Q (B), or rHCII^R189H (C) in PBS. After 2 rinses with buffer, the sections were stained with a polyclonal goat anti-HCII IgG. The section in panel D was treated with chondroitin ABC-lyase to degrade DS prior to incubation with rHCII^WT. Arrow indicates internal elastic lamina; arrowhead, external elastic lamina. rHCII^WT and rHCII^K173Q bound strongly to sites in the adventitia.