Mechanisms underlying the suppression of adjuvant-induced arthritis by 6-mercaptopurine.

Daily oral administration of 6-mercaptopurine suppressed the development of the secondary (immune) lesions of adjuvant arthritis in a dose-related manner. The degrees of arthritis suppression corresponded closely to suppressions of concurrent development of the humoral and the cellular immune response to El4 cells. A short course of therapy during the sensitization period (day - 1 to day 5 when the day of adjuvant injection is designated as day 0) appeared to be almost as effective as continued daily dosing (day - 1 to day 15). The drug did not influence the development of the primary (nonimmune) lesions of adjuvant arthritis at all dosage levels investigated. Chronic pretreatment with 10 mg/kg/day PO for 17 days had no effect on the development of carrageenin-induced acute inflammation in the rat. The suppression of adjuvant arthritis by 6-mercaptopurine, unlike suppression by cyclophosphamide, appears to result primarily from its suppressive action on the immune response.