Antigen‐induced arthritis

During the acute phase of antigen-induced arthritis, cartilage was obtained from five different sites within the joint, and chondrocyte activity was assessed by autoradiography of sections labeled with 35S-sulfate. There was a marked inhibition of chondrocyte proteoglycan synthesis in all weight-bearing areas; in addition, the complete superficial layer of cells and many mid-zone cells in these areas were completely inactive. Electron microscopy showed that the inactive surface cells had degenerated completely, and that many mid-zone cells contained an accumulation of intracytoplasmic filaments and were depleted in biosynthetic organelles. A biochemical study of the inhibition showed that: 1) the incorporation of 35S-sulfate and 3H-acetate into glycosaminoglycans was inhibited to a similar extent; 2) the inhibition of glycosaminoglycan synthesis could not be reversed either by the addition of benzyl-beta-D-xyloside to incubations or by maintenance of the cartilage in organ culture for 6 days; 3) the inhibited chondrocytes exhibited a decreased ability to secrete proteoglycans into the extracellular fraction of the cartilage.