A radioreceptor assay for TNF alpha-binding proteins.

A radioreceptor assay for tumour necrosis factor alpha (TNF alpha)-binding proteins was development that is suitable for use with synovial fluids and sera. This assay, an alternative to the commonly used enzyme-linked immunosorbent assays (ELISAs), is not specific for soluble tumour necrosis factor alpha receptors (sTNF-R), but detects any molecules that might compete with TNF alpha for receptor binding. It also detects molecules that might bind TNF alpha and thereby interfere with subsequent binding to receptor. In a preliminary study, the assay was used to determine levels of TNF alpha-binding activity in a test group of synovial fluids from patients with rheumatoid arthritis (RA), osteoarthritis (OA) or psoriatic arthritis (PA). Levels of binding activity were much higher than those reported for sTNF-R alone in other studies [1, 2]. Our results indicated that there may be other molecules associated with the inflamed synovium that can interfere with the binding of TNF to its receptors and so attenuate its effect in diseases such as RA.