Rheumatoid pannus formation: synovial cell attachment to the surface of cartilage

Abstract

As a part of the rheumatoid synovial tissue reaction, proliferating synovial cells penetrate the cartilage in the form of a pannus, and cartilage destruction takes place in the zone between the cells and cartilage. The cellular origin of rheumatoid pannus has been debated by many investigators, and it is accepted that fibroblast proliferation, endothelial cells proliferation and monocyte chemotaxis are probably involved. It has been observed that fibroblasts in the pannus share properties of the fibroblasts and chondrocytes. Mast cell activation is frequently associated with proinflammatory cytokine and metalloprotease expression, suggesting an important role for the mast cell in mediating matrix degradation. The mechanism of interaction of polymorphonuclear leukocytes with immune complexes trapped in rheumatoid cartilage resembles that associated with phenomenon of frustrated phagocytosis. Increased levels of IL-1 in the rheumatoid joint may play an important role in joint destruction by stimulation of pannus formation through induction of synovial cell attachment to the articular surface. Synovial cell attachment to cartilage may be the initial step in pannus formation. We have recently shown that the increased expression of VLA-5 and ICAM-1 at the cartilage-pannus junction may result from the interaction of synovial mononuclear cells with matrix proteins. Therefore, we have raised the possibility that VLA-5 may facilitate the growth of pannus by virtue of its ability to react with fibronectin with resulting proliferation of the synoviocytes of the pannus. Further study will be needed in order to understand the precise mechanism of cartilage erosion and pannus formation in the various arthritic disorders.

Key words::

• Pannus formation
• synovial cell attachment
• adhesion molecules
• integrins
• cell-ECM interaction