Characterization of cells from pannus-like tissue over articular cartilage of advanced osteoarthritis

Objective: To identify the characteristics of cells isolated from pannus-like soft tissue on osteoarthritic cartilage (OA pannus cells), and to evaluate the role of this tissue in osteoarthritis (OA). Methods: OA pannus cells were isolated from pannus-like tissues in five joints obtained during arthroplasty. The phenotypic features of the isolated cells were characterized by safranin-O staining and immunohistochemical studies. Expression of MMP-1, MMP-3 and MIMP-13 was also assessed using reverse transcriptase-polyme rase chain reactions (RT-PCR), enzyme-linked immunosorbent assay (ELISA) and immunocytochemistry. Results: Foci and plaque formation of pannus-like tissue over cartilage surface were found in 15 of 21 (71.4%) OA joints macroscopically, and among them, only five samples had enough tissue to be isolated. OA pannus cells were positive for type I collagen and vimentin, besides they also expressed type 11 collagen and aggrecan mRNA. Spontaneous expression of MMP-1, MMP-3 and MMP-13 was detected in OA pannus cells. Similar or higher levels of MMPs were detected in the supernatant of cultured OA pannus cells compared to OA chondrocytes, and among these MMP-3 levels were relatively higher in OA pannus cells. Immunohistochernically, MMP-3 positive cells located preferentially in pannus-like tissue on the border of original hyaline cartilage. Conclusion: Our results showed that OA pannus cells shared the property of mesenchymal cells and chondrocytes; however, their origin seemed different from chondrocytes or synoviocytes. The spontaneous expression of MMPs suggests that they are involved in the articular degradation in OA. (C) 2003 OsteoArthritis Research Society International. Published by Elsevier Ltd. All rights reserved.