An assay for estimating the cytotoxicity of synovial fluid from patients with rheumatoid arthritis.

The joint is the prime site of involvement in rheumatoid arthritis: the synovium showing lymphocytic involvement and damage. The synovial fluid shows evidence of inflammation such as increased neutrophils and raised CRP. Application of a cell-free extract of serum or synovial fluid from patients with rheumatoid arthritis, or serum from normal individuals on to 111indium oxine radiolabelled endothelial cells and fibroblasts, promotes the release of the isotope as a result of cell damage and death (cytotoxicity). In paired samples, synovial fluid was consistently more cytotoxic than rheumatoid serum. There was no difference in the cytotoxicity of rheumatoid serum or normal serum. These results demonstrate the presence of soluble factors in synovial fluid, which are capable of destroying cells, typical of those found in the synovial cavity, in blood vessels and in connective tissue generally. This system may prove to be a useful model of inflammatory damage.