Demonstration of antibody specificity. High magnification views of articular cartilage from a 69-year-old OA patient, showing cleavage of type II collagen by collagenases (C1,2C and C2C) and cathepsin K (C2K). Control (A) was prepared by prior absorption of the antisera with the immunizing peptides. Immune staining (B) using unabsorbed antibodies. Bar = 200 μm.