Enhanced cytotoxicity in the rheumatoid joint

The cytotoxic cytokines, tumor necrosis factor-α or cachectin and lymphotoxin (LT), are mediators of bone resorption and of inflammation and may have relevance in rheumatoid arthritis. Using mononuclear cells (MC) isolated from matched peripheral blood (PB) and synovial fluid (SF) of 13 patients with rheumatoid arthritis, we examined the generation of cytotoxic activity in a bioassay capable of detecting both TNF and LT. Synovial fluid mononuclear cells (MC) released significantly more cytotoxic activity than did matched PBMC, both spontaneously and following activation with phytohemagglutinin P (PHA). When PB and SFMC were stimulated with the combination of PHA plus phorbol-12-myristate acetate (PMA), the resulting culture supernatants possessed comparable cytotoxic activity. Neutralization studies employing anti-cytokine antibodies indicated that TNF represented 43 and 59% of the cytotoxic activity in the PHA plus PMA-induced culture supernatants from PB and SF, respectively. Since no inhibition was noted with antibodies to LT, the nature of the remaining approximately 50% of the cytotoxic activity was not determined. In PB and SF culture supernatants, obtained both spontaneously and following PHA activation, the concentration of TNF measured by ELISA significantly correlated with the level of cytotoxicity. As with the cytotoxic activity, the concentration of TNF was greater in the PHA-stimulated supernatants from SF than from PB. These observations suggest that TNF in the SF may contribute to the inflammation and bone destruction observed in rheumatoid arthritis.