Electron microscopic demonstration of immunoglobulin deposition in rheumatoid cartilage

Horseradish peroxidase (HRPO) conjugated with goat antihuman IgG, goat antihuman IgM, and aggregated human IgG has been used as a enzymatic marker to stain IgG, IgM, and rheumatoid factor in rheumatoid cartilage. When Hrpo-anti IgG and HRPO-anti IgM were used, immunoglobulin deposits were not observed in nonrheumatoid cartilage. However 7 of 8 rheumatoid cartilage specimens stained with HRPO-anti IgG showed electron-dense deposits. Three rheumatoid specimens stained with HRPO-anti IgM showed similar findings. Both of 2 rheumatoid specimens also stained positively with HRPO conjugated with aggregated IgG, a finding indicating that rheumatoid factor was present. The deposits were seen between the collagen fibers of the superficial layer of the cartilage to a maximal depth of 22 mu from the surface (average: 7 mu). The amorphous fibrinous material on the surface of the cartilage was also stained. The demonstration of IgG, IgM, and rheumatoid factor in the superficial zone of rheumatoid cartilage suggests that immune complexes are deposited in the cartilage in this disease.