Immunodiffusion studies on synovial fluid from patients with rheumatoid arthritis: the reaction of fibrinogen with a streptococcal extract.

Synovial fluids (83.3%) from patients with rheumatoid arthritis gave a positive reaction when examined by immunodiffusion against a Lancefield extract of Group A Type 12 streptococci. None of the patients with osteoarthrosis reacted positively. An antiserum was prepared to the material in synovial fluid reacting with the streptococcal extract. This antiserum reacted positively with all synovial fluids tested including the osteoarthrosis patients. It also reacted with all plasma samples tested but only with a few (18.2%) of serum samples. Immunodiffusion and absorption experiments demonstrated that the material reacting with the streptococcal extract was fibrinogen. Of 12 other streptococci examined only one, a Group C organism, gave a similar positive reaction with synovial fluids.