Mechanisms Underlying the Suppression of Adjuvant‐Induced Arthritis by 6‐Mercaptopurine

Abstract

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 El, 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.6-Mercaptopurine is known to have both immunosuppressive and antiinflammatory properties (1,2). The drug has been shown to suppress adjuvant-induced polyarthritis in the rat, a disease thought to be the result of a delayed hypersensitivity response to bacilli or their components (3,4), presumably by a combination of immunosuppressive and antiinflammatory actions (5,6). This study was undertaken to determine the relative contributions of antiinflammatory and immunosuppressive activities in the suppression of adjuvant arthritis by 6-mercaptopurine. MATERIALS AND METHODSMaintenance of El, Cell Line. The El, tumor cell line was a gift from Dr. J. Wunderlich, NIH, Bethesda, MD. El, cells were maintained by passage in syngeneic C57/bl 6 mice (Jackson Laboratories, Bar Harbor, ME). The cells (2 X lo7)were injected intraperitoneally on day 0. On day 7, approximately 3-5 X 108 cells per mouse were harvested from the peritoneum, and after washing with Hanks' minimum essential medium (HMEM), they were used either for replanting the cell line, for immunization, or as target cells in immune assays.Polyimmune Adjuvant Arthritis. Adjuvant arthritis was produced by a single subcutaneous injection of 1 mg of Mycobacterium butyricum (Difco Laboratories, Detroit, M I ) suspended in 0.1 ml of mineral oil into the right hind paw of male Lewis inbred rats (Microbiological Associates, Bethesda, MD) weighing between 235 and 250 g. A I .O ml suspension of El, cells ( 1 X 108 cells/ml) in HMEM was injected intraperitoneally immediately after the subplantar injection of adjuvant. The paw volume was measured by the method of Winter et al(7) on days 0,4, and 16 (or 22) with respect to the injection of adjuvant. All rats were treated with either saline or drug (PO or IM) daily from day -1 to day + 15 unless otherwise noted. After paw volume was measured on day 16, a sample of blood was taken and the spleen was removed. The serum and spleen cells were used to measure immune response.

An unusual profile of activity of a new basic anti-inflammatory drug, timegadine

“…beginning on the day of adjuvant injection was ineffective. CHANG [18] and WALZ et al [19] found that phenylbutazone administered for 4 days after adjuvant was also ineffective. By contrast an identical dosing regime with cyclophosphamide and 6-mercaptopurine caused significant inhibition on day 21 post-adjuvant [18,19].…”

“…CHANG [18] and WALZ et al [19] found that phenylbutazone administered for 4 days after adjuvant was also ineffective. By contrast an identical dosing regime with cyclophosphamide and 6-mercaptopurine caused significant inhibition on day 21 post-adjuvant [18,19]. The observation that a short course of treatment with timegadine at the time of adjuvant injection was almost as effective as continued daily dosing in inhibiting the swelling of the non-injected paw may suggest that this compound affects early events in the pathogenesis of adjuvant arthritis which later results in the development of the secondary lesions.…”