Intracellular collagen fibers at the pannus-cartilage junction in rheumatoid arthritis.

Sections of the pannus-articular cartilage junction from a patient with rheumatoid arthritis (RA) were prepared for electron microscopy. Cells at this interface contained membrane-bound collagen fibrils, apparently in various stages of digestion. Previous studies have demonstrated intracellular collagen fibrils at sites of very active and rapid collagen resorption. It is suggested that at certain times in certain patients with RA, phagocytosis of cartilage collagen fragments and subsequent intracellular digestion may serve as a supplemental pathway to extracellular collagen degradation.