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The short-term and long-term effects on the growth zone in articular cartilage of transforming growth factor-beta 1 and platelet-derived growth factor-BB injected intraarticularly into the knee joint of growing rats were investigated. The changes induced by five injections of 0.5 micrograms of transforming growth factor-beta 1 included a rapid decrease in the size and number of hypertrophic cells and an enhanced subchondral bone formation. The changes were most marked in the patella but were also apparent in the tibia and femur. The proliferating cells became swollen and lost their normal organization. From the seventh day of the experiment to about 3 weeks, the matrix stained intensely with safranin O for proteoglycans. The alterations induced by transforming growth factor-beta also included synovial fibroplasia and synovitis, consisting predominantly of mononuclear cells. Localised necroses in the cartilage sometimes appeared after 21 days. In long-term studies, destroyed cartilage was found in three of six rats and partial ossification of the joint cartilage was found in two after 90 and 180 days. Ossicles developed in the tendons in all six patellae. Injection of platelet-derived growth factor-BB resulted in an early and transitory minor increase in the osteogenic activity in the zone between cartilage and red bone marrow and later produced an ossicle in one of four tendons. None of the other changes noted after injection of transforming growth factor was observed.

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Monoclonal antibodies to 3 different epitopes on native type I1 collagen were used for immunohistochemical analysis of antigenic determinants that are exposed in the cartilage and synovial tissue obtained from patients with rheumatoid arthritis (RA) and osteoarthritis (OA). Two of the monoclonal antibodies reacted with cartilage from both OA and RA joints, but not with that from normal joints. The third monoclonal did not stain any of the cartilage sections. The 2 positive antibodies also reacted with cartilage fragments in the synovial tissue of both RA and OA joints, and in RA pannus tissue, the antibodies showed intracellular staining in many class I1 transplantation antigen-expressing synovial cells lying close to the damaged cartilage.The cartilage lesions that are seen in patients with rheumatoid arthritis (RA) and those with osteoarthritis (OA) result from processes which, at least in RA, are due to inflammatory reactions in the synovial tissue (for review, see ref. 1). The demonstration of an