Impaired suppressor cell activity due to surface sulphydryl oxidation in rheumatoid arthritis

Rheumatoid arthritis is a chronic inflammatory disorder with considerable evidence of impaired regulation of the immune response, including defective suppressor cell function, especially in the synovial membrane. We have investigated whether oxidation of cell surface thiols might be responsible for these defects and whether such cell function may be modulated towards normal by treatment with a sulphydryl-reactive drug, D-penicillamine. Using healthy mononuclear cells treated with an impermeant thiol blocker, induction of suppressor activity by incubation with the lectin Con A was not dependent on surface sulphydryl groups but suppressor activity was abolished by thiol blockade after Con A stimulation. Peripheral blood mononuclear cells from patients with active rheumatoid disease showed impaired Con A-induced suppressor activity which was enhanced to near-normal levels by incubating the rheumatoid cells with a sulphydryl reducing agent, 2-mercaptoethanol, or D-penicillamine. Con A-stimulation of cells from patients treated with intramuscular gold or D-penicillamine generated more active suppression than those from patients receiving non-steroidal drugs only. Mononuclear cells from patients with other chronic inflammatory joint diseases showed normal Con A-induced suppressor activity. These data support the conclusion that surface thiols on mononuclear cells in rheumatoid arthritis are reversibly oxidized by the disease process. This gives rise to aberrant cell function including impaired suppressor activity. Such a mechanism may be at least partly responsible for the defective immunoregulation seen in rheumatoid patients and thus be a relevant target for thiol containing antirheumatic drugs.