Study of enzyme inhibitors in the rheumatoid pannus-cartilage area

Immunoperoxidase studies were carried out on the pannus-cartilage junction (PCJ) of patients with rheumatoid arthritis (RA) and psoriatic arthritis to investigate the distribution of the enzyme inhibitors alpha 2 macroglobulin (alpha 2 M) and alpha 1 antitrypsin (alpha 1 AT). Comparisons were made with the equivalent synovial cartilage junctional area in osteoarthritis (OA). In all 12 patients with RA, prominent deposits of alpha 2 M and alpha 1 AT were found within the PCJ whereas in OA patients and the case of psoriatic arthritis fewer or no deposits were seen. Inhibitors were localised in pannus synovial lining cells, perivascular inflammatory cells, macrophage and fibroblast-like cells invading the cartilage as well as along the junctional cartilage matrix and in the adjacent pannus-free cartilage. Deposits of immunoglobulins were found in similar areas to enzyme inhibitors. The presence of enzyme inhibitors at the PCJ suggests that this area is not unprotected against enzymatic attack. Thus the concept that pannus is a prime area for cartilage damage because aggressive, invasive cells release destructive enzymes in an environment free from inhibitors should be reviewed.