Antigen-induced and zymosan-induced arthritis in mice: studies on in vivo cartilage proteoglycan synthesis and chondrocyte death.

The influence of joint inflammation on patellar hyaline articular cartilage was studied in mice. Antigen-induced and zymosan-induced arthritis were used as models for immunologically and non-immunologically induced joint inflammation. The contribution of newly formed proteoglycan to the cartilage proteoglycan content, as measured by labelling of the cartilage after i.v. administration of 35S-sulphate, was decreased in parallel with the severity of inflammation during both zymosan-induced and antigen-induced arthritis. The decreased 35S content of the cartilage was due to inhibition of synthesis rather than breakdown of newly synthesized proteoglycan, since no accelerated release of 35S from arthritic cartilage could be demonstrated in vitro. Antigen-induced arthritis was associated with progressive chondrocyte damage. Loss of chondrocytes was consistently found in the central part of the patella, without nearby presence of pannus. It would appear that, in addition to enzymatic breakdown of cartilage, other phenomena are important in cartilage destruction: inhibition of proteoglycan synthesis and chondrocyte death, apparently unrelated to pannus formation.