Generation of effector T cells in Hymenolepis nana-infected, FK-506-treated BALB/c mice.

FK-506 administered into mice daily at a dose of 10.0 mg/kg (but not 1.0 and 5.0 mg/kg) caused suppression of protective immunity to Hymenolepis nana, when the agent was injected intraperitoneally during the induction phase of protective immunity. Daily administration of 10.0 mg/kg FK-506, during the course of larval development from challenge, also suppressed protective immunity. Inhibition of protective immunity was only observed in mice that received FK-506 for 6 days at a daily dose of 10.0 mg/kg and were challenged 24 h after the final FK-506 injection. FK-506 did not inhibit formation of effector cells that mediate delayed-type hypersensitivity (DTH) to H. nana egg antigen when the agent was administered intraperitoneally at a dose of 10.0 mg/kg/day for 6 days before cell preparation. However, FK-506 did inhibit DTH effector cell activation when cells prepared from infected, saline-injected mice were transferred into 10.0 mg/kg FK-506-treated recipient mice. These results strongly indicate that FK-506 cannot inhibit the generation of effector cells but will suppress their function in vivo.