Role of the chondrocytes in the breakdown of pig articular cartilage induced by complement-sufficient antiserum to pig erythrocytes.

Previous work showed that in organ culture pig articular cartilage is not affected by complement-sufficient antiserum to pig erythrocytes (AS plus C') unless it is associated with soft connective tissue. In the presence of synovial tissue the matrix becomes depleted of proteoglycan and may finally disintegrate. Immunoglobulin fails to enter normal cartilage matrix, but penetrates depleted matrix and reacts with the surfaces of the chondrocytes. The present experiments were made to see whether the breakdown of partially depleted cartilage matrix would progress in AS plus C' after removal of the synovial explant. Affronted explants of articular cartilage and synovial tissue were cultivated in AS plus C' for 10 days (primary cultures). The synovial tissue was then removed and the isolated cartilage maintained for a further period either in AS plus or C' or in one of a variety of control media (SECONDARY CULTURES). The behavior of the isolated cartilage during the secondary culture period depended on the degree of breakdown attained at the end of the primary period. If only proteoglycan but not collagen had been seriously depleted, degradation of the matrix did not progress in AS plus C' and slight regeneration of metachromatic materal sometimes took place; regneration of matrix was greater after transfer to control medium. If collagen as well as proteoglycan had been destrobyed, the chondrocytes assumed a fibroblastic form, their surfaces no longer reacted with IgG antibody, and in secondary culture they failed to regenerate new matrix.