The relationship between cell-mediated immunity and cartilage degradation in antigen-induced arthritis in the rabbit

The relative contributions of cellular and humoral immunity to cartilage destruction in chronic arthritis has been investigated in a model of chronic synovitis in the rabbit. In this model, antigen-induced arthritis, immunization with ovalbumin in Freund's complete adjuvant (FCA) followed by intra-articular injection of this protein produces a chronic synovitis associated with loss of proteoglycan from articular cartilage. In addition, the synovial lining cell population is metabolically activated. Similar treatment of animals immunized with ovalbumin in Freund's incomplete adjuvant (FIA) produced a resolving arthritis which initially (over the first 7 days) appears to be identical to that in FCA-immunized animals, apart from the lack of activation of synovial lining cells. Following this initial synovitis the joints return to apparent normality apart from a persistent 'low grade' synovitis consisting mainly of a plasma cell infiltrate. The most striking finding in the FIA-immunized animals is the rapid loss (greater than 30% by day 7) and recovery of proteoglycan from the matrix of articular cartilage. These findings show that the perpetuation of chronic destructive synovitis in the rabbit requires the presence of active cellular immunity.