Deleterious interactions of immune complexes with tibial cartilage of antigen-induced arthritic rabbits. II: Chondrocyte degradation.

The observations of immune complex (IC) deposition in the surface of rheumatoid arthritis (RA) cartilage, in conjunction with degradative changes in superficial and midzone chondrocytes, raised the question of causal relationships. In antigen-induced arthritis in rabbits, cartilage degradation occurred in association with IC deposition and is accompanied by chondrocyte damage. Superficial and midzone chondrocytes in rabbit tibial cartilage of arthritic joints, induced by bovine serum albumin (BSA) or ferritin (Fn), were examined by electron microscopy during the evolution of the arthus response. The first cell changes were noted at six hours, by which time superficially formed IC had begun to extend into the matrix. Elongated cytoplasmic footlets, numerous lysosomes, and lipid droplets occurred initially. By 24 hours, concomitant with the deeper extension of surface IC, prominent changes in chondrocytes of both superficial, and midzones progressed to ultrastructural evidence of cell death. The pinocytosis of electron-dense amorphous materials, which included IC, preceded degradation. These data suggest that the observed cytopathology is a manifestation of locally deposited IC.