Astrocytes have the capacity to secrete or respond to a variety of cytokines including IL-1, IL-6, IL-3, and TNF-α. In this study, we have examined the capacity of astrocytes to secrete TNF-α in response to a variety of biologic stimuli, particularly cytokines such as IL-1 and IFN-γ, which are known to be present in the central nervous system during neurologic diseases associated with inflammation. Rat astrocytes do not constitutively produce TNF-α, but have the ability to secrete TNF-α in response to LPS, and can be primed by IFN-γ to respond to a suboptimal dose of LPS. IFN-γ and IL-1β alone do not induce TNF-α production, however, the combined treatment of IFN-γ and IL-1β results in a striking synergistic effect on astrocyte TNF-α production. Astrocyte TNF-α protein production induced by a combined treatment of either IFN-γ/LPS or IFN-γ/IL-1β occurs in a dose- and time-dependent manner, and appears to require a 'priming signal' initiated by IFN-γ, which then renders the astrocyte responsive to either a suboptimal dose of LPS or IL-1β. Astrocyte TNF-α production by IFN-γ/LPS stimulation can be inhibited by the addition of anti-rat IFN-γ antibody, whereas IFN-γ/IL-1-induced TNF-α production is inhibited by antibody to either IFN-γ or IL-1β. Polyclonal antisera reactive with mouse macrophage-derived TNF-α neutralized the cytotoxicity of IFN-γ/LPS and IFN-γ/IL-1β-induced astrocyte TNF-α, demonstrating similarities between these two sources of TNF-α. We propose that astrocyte-produced TNF-α may have a pivotal role in augmenting intracerebral immune responses and inflammatory demyelination due to its diverse functional effects on glial cells such as oligodendrocytes and astrocytes themselves.