Figure 13: IHC of lubricin (PRG4) in the articular cartilage. Control (A), and MMx (B) knee joint. Human OA knee articular cartilage, served as positive control (C) and as negative control (D). A1/A2, B1/B2, C1/C2 and D1 are higher magnification of boxed area in A, B, C and D, respectively. Lubricin showed expression mainly in the superficial zone of articular cartilage in the control knee (A, A1, A2). However, in MMx knee, lubricin expression was present in the articular cartilage except in the fibrillation area (arrowheads) at the medial aspect of tibia where superficial/transitional zone and part of deep zone of articular cartilage is damaged. Human OA knee articular cartilage, serving as positive control, shows lubricin expression in the superficial zone and transitional zone (C, C1, C2). Human OA knee articular cartilage, serving as negative control, did not show staining (D, D1).