Tumour necrosis factor activity in joint fluids from rheumatoid arthritis patients.

Although tumour necrosis factor (TNF) was first studied as an anti-cancer agent it is now recognized as a potent mediator of inflammation and could potentially play a role in rheumatoid arthritis. In this study TNF activity has been sought in fluids from arthritic joints. TNF was assayed by a well established bioassay which depends upon cytolysis of particular tumour cell lines and which has a limit of detection of c. 25 pg/ml. Of the 92 joint fluids tested (70 rheumatoid and 22 others) only three had demonstrable TNF activity. Despite this, joint fluid cells from all 14 patients tested (12 rheumatoid and two others) had the ability to synthesize TNF on stimulation in vitro. Subsequently it was shown that joint fluids contain a macromolecule which inhibits TNF activity in cytolytic assays and which may mask low levels of TNF activity in joint fluids.