Cytotoxic effects of rheumatoid arthritis sera on chondrocytes

Human sera from patients with rheumatoid arthritis (RA) and also from healthy donors were found to be toxic to cultured chondrocytes. Immunoglobulins were found to bind to the surface of cultured cells and cells in chicken sternal cartilage, as detected by indirect immunofluorescence. In vitro, cell detachment from the substrate was caused by the incubation of chondrocyte monolayers with 5 per cent and less RA serum. Serum treatment caused cytotoxic degradation of the cells. This could be quantified by a chromium release assay. Heat inactivation of the serum abolished the cytotoxicity. The extent of the cytotoxic reaction was related to the complement content of the serum and also to the intensity of the disease, as determined by the Ritchie-index. Other cell types, as chondrosarcoma cells, normal fibroblasts and corneal epithelium, were not affected by RA sera.