Destruction of rabbit knee hyaline cartilage associated with surface antigen-antibody interaction during the Arthus reaction of antigen-induced arthritis.

Ultrastructural changes occurring in rabbit hyaline cartilage were studied during the early stages of antigen-induced arthritis. After one hour, small deposits of electron-dense material (EDM) were noted at depths up to about 3 micron from the surface. During subsequent stages, the number of EDM deposits did not increase, but by 12 hours they had grown to large aggregates. At the surface, extensive deposition and growth eventually resulted in exfoliation of surface layers of cartilage, exposing a fissured matrix. From previous evidence, EDM has been equated with immune complexes (antigen and homologous antibody). The mechanism of cartilage destruction is therefore closely linked to reactions of antigen and antibody within the hyaline cartilage. Mechanical and/or biochemic processes may be involved, but cells do not appear to participate in the destructive process, at least not in regions remote from pannus.