Immunohistochemical detection of cartilage intermediate layer protein 1 in the synovial membrane of patients with knee complaints

Cartilage intermediate layer protein 1 (CILP-1) is a structural component of the cartilage extracellular matrix. As CILP-1 localization outside the articular cartilage is noted, we aimed to detect CILP-1 in the synovial membranes. Synovial membrane samples were collected from 30 patients, who formed a subset of an extensive osteoarthritis (OA) study and who had undergone knee arthroscopy due to knee complaints. Immunohistochemistry was used to detect CILP-1 in the synovial membranes. Double immunofluorescence staining was applied in order to confirm the presence of CILP-1 in synovial macrophages (CD68 positive cells). Immunohistochemical staining of CILP-1 was found in cells of synovial membrane as well as in blood vessels, particularly in medial layer. However, CILP-1 staining was not seen in all cells or blood vessels. No correlation was found between the semi-quantitative score of CILP-1 staining and histological score of synovitis. Conclusions: The CILP-1 was detected in the synovial membranes and was demonstrated to be localized in macrophages and in synovial blood vessels. However no correlation between semi-quantitative assessment of CILP-1 staining and histological score of synovitis could be shown.