Rheumatoid arthritis is a chronic inflammatory disease leading to alterations of the extracellular matrix in tendons, ligaments, and cartilage. The structural changes of the collagenous systems in rheumatoid connective tissues are largely unknown, however.
Thirty four samples of menisci, 36 cruciate ligaments, and four tendons were taken during joint surgery in patients with rheumatoid arthritis. Eighteen menisci, 35 ligaments, and 30 tendons obtained at necropsy served as a control group. The extracellular matrix in the two groups was analysed by the combined use of transmission and scanning electron microscopy, immunohistochemistry with monoclonal antibodies recognising collagen types IV and VI, and ultramorphometry.
Normal tendons and ligaments predominantly showed a unidirectional fibril arrangement. Whereas type IV collagen showed a positive staining pattern along all basement membranes, type VI collagen formed fine, filaments aligned in parallel. In patients with rheumatoid arthritis a significant reduction of the mean diameter of the collagen fibrils was found owing to the presence of thin collagenous fibrils 20-60 nm in diameter. Most of these fibrils showed considerable changes in their arrangement with irregular courses (so-called interfibrillar dysplastic collagen). Up to 410 nm thick frayed fibrils with irregular outlines (spiralled collagen) and intracellular collagen forms were found in rheumatoid tissues. In addition, atypical thick collagenous structures with 41 nm periodicity (Luse bodies) were detected in the matrix. The upregulation of type IV collagen in rheumatoid arthritis was associated with an increase in the vascular density. The expression of type VI collagen was upregulated in fibrotic zones.
The dramatic ultrastructural collagen changes lead to a structural and functional insufficiency of the extracellular matrix in rheumatoid connective tissues. The results suggest that collagen alterations may contribute to the development of tendon and ligament ruptures in rheumatoid arthritis.