Defective monocyte cytotoxicity in rheumatoid arthritis: a correlation with disease activity and reversal by levamisole.

The cytotoxic activities of human blood mononuclear cells against certain established cell lines were evaluated prospectively in 17 patients with rheumatoid arthritis before and after treatment with low (150 mg per week) and moderate doses (300 mg per week) of levamisole. Spontaneous or "natural" killer activity (NK) and antibody-dependent cellular cytotoxicity (ADCC) of plastic adherent cells ("monocytes") and lymphocytes were studied. We report a selective cytotoxic defect in monocyte NK and a correlation of this defect with severely active disease. The patients with the most severe defect responded to low-dose levamisole, but others with normal values did nor respond as well to treatment. This cytotoxic defect may be an important pathogenetic factor in rheumatoid arthritis and this new assay may be helpful in selecting candidates who are most likely to respond to levamisole.