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Down-regulation of mammalian cytokine production has been demonstrated during tick feeding. To examine the hypothesis that reconstitution of cytokines during tick feeding could facilitate immune containment of Borrelia burgdorferi, the following experiments were done. C3H/HeJ mice were given cytokines for 10 days after Ixodes scapularis attachment. At day 21, ear biopsies were analyzed for B. burgdorferi. Polymerase chain reaction analysis indicated a protection rate of 95% in mice receiving tumor necrosis factor (TNF)-alpha. Mice that received interleukin (IL)-2 or interferon (IFN)-gamma had infection rates of 30%-45% compared with 83% for untreated controls. No correlation was noted between neutralizing antibody, reactivity by Western blot, and subsequent protection. Culture of B. burgdorferi in cytokine-conditioned media indicated that TNF-alpha, IFN-gamma, and IL-2 were not cytotoxic for B. burgdorferi. These data suggest that cytokine-induced protection from B. burgdorferi infection was immune-mediated and that cellular immunity may be associated with protection from I. scapularis-induced infection.