ABSTRACT
C ytokines are a family of growth factors that are secreted by the cells of the immune system. The family includes interleukins (IL), interferons (IFN), tumor necrosis factors (TNF), chemokines and other growth factors. Cytokines stimulate both the humoral and cellular immune responses as well as the activation of phagocytic cells and are generally associated with inflamma tion, immune activation, cell differentiation and cell death. They have diverse actions and are rapidly induced in response to tissue injury, infection or inflam m ation . T h e ir role as m ediators and in h ib ito rs o f diverse form s o f neurodegeneration is increasingly recognized. Cytokines are induced in response to brain injury and can either induce, mediate, inhibit, or exacerbate cellular injury and repair. Several proinflammatory cytokines, notably tumor necrosis factor-а (TN F-a), have been shown to mediate diverse forms of experimental neurodegeneration, and both neurotoxic and neuroprotective actions have been reported. Here we review evidence for the contribution o f cytokines to neurodegeneration, focusing primarily on tumor necrosis factor (TNF), which not only contributes to neuronal injury but may also exert protective effects. Since the mechanism of action of TNF and its interactions with various mol ecules in neurodegeneration is largely unknown, questions regarding these pro cesses are of paramount importance to neurobiologists. Understanding the pre cise role of TNF in neurodegeneration is likely to have direct relevance in the search for potential treatments for neurodegenerative disease.
