The effect of FK506 (FK), a potent immunosuppressive agent, on collagen arthritis in Sprague-Dawley rats was investigated. A single subcutaneous injection of FK at a dose of 10mg/kg on the same day as type II collagen immunization, suppressed the development of arthritis as well as humoral and delayed-type hypersensitivity (DTH) skin test responses to type II collagen, possibly by interfering with IL-2 or IL-2 receptor. Additional studies demonstrated that FK treatment after the disease onset, a significant suppression of the disease was obtained with single injection at the same dose. These results appear to be attributable at least in part to a suppressive effect of FK on a later phase than IL-2 phase.
