Tissue inhibitors of metalloproteinases (TIMPs) are a family of closely related proteins that inhibit matrix metalloproteinases (MMPs). In the central nervous system (CNS), TIMPs 2, 3, and 4 are constitutively expressed at high levels, whereas TIMP1 can be induced by various stimuli. Here, we studied the effects of constitutive expression of TIMP1 in the CNS in transgenic mice. Transgene expression started prenatally and persisted throughout lifetime at high levels. Since MMP activity has been implicated in CNS development, in proper function of the adult CNS, and in inflammatory disorders, we investigated Timp1-induced CNS alterations. Despite sufficient MMP inhibition, high expressor transgenic mice had a normal phenotype. The absence of compensatory up-regulation of MMP genes in the CNS of Timp1 transgenic mice indicates that development, learning, and memory functions do not require the entire MMP arsenal. To elucidate the effects of strong Timp1 expression in CNS inflammation, we induced experimental allergic encephalomyelitis. We observed a Timp1 dose-dependent mitigation of both experimental allergic encephalomyelitis symptoms and histological lesions in the CNS of transgenic mice. All in all, our data demonstrate that (1) long-term CNS expression of TIMP1 with complete suppression of gelatinolytic activity does not interfere with physiological brain function and (2) TIMP1 might constitute a promising candidate for long-term therapeutic treatment of inflammatory CNS diseases such as multiple sclerosis. (Am J Pathol