Differential tumor necrosis factor alpha expression by astrocytes from experimental allergic encephalomyelitis-susceptible and -resistant rat strains

TNF-a Protein Production by Astrocytes from EAE-resistant and -susceptible Rat Strains. We examined TNF-a protein production by astrocytes from Lewis and BN rat strains in response to three different stimuli. Lewis and BN astrocyte cultures were treated with varying concentrations of LPS (1-10,000 ng/ml) with and without IFN-y (100 U/ml), or IFN-y (1-1,000 U/ml) plus RAO (1,000 U/ml) for 18 h, at which point the supernatants were harvested and assayed for TNF-a production . As shown in Fig. 1 , BN astrocytes produced TNF-a in response to LPS in a dose-dependent manner. Pretreatment of these cells with IFN-y, then LPS, did not result in significant enhancement of TNF-a production. Even more striking was the observation that BN astrocytes secreted neglible amounts of TNF-a in response to the stimuli of IFNy/IL 10 . This induction pathway was previously shown to be dependent on a priming signal generated by IFN-y, then subsequent exposure to 11,10 (11) . Lewis astrocyte cultures exhibited a different induction pattern with respect to TNF-a production . Lewis astrocytes responded poorly to LPS alone at all concentrations tested, yet when pretreated with IFN-y, then exposed to LPS, TNF-a protein production increased significantly (Fig . 2) . Lewis astrocytes also produce TNF-a in response to IFN-y/IIr10, in the range of what was previously observed for astrorytes from the outbred rat strain Sprague-Dawley (11). The Lewis x BN Ft rats show susceptibility to EAE compared with the fully resistant BN rat, however, disease severity in the Fl strains is less than that observed for Lewis rats. The Ft astrorytes produced low amounts of TNF-a in response to LPS, and IFN-y pretreatment significantly enhanced LPS-induced TNF-a production (Fig. 3) . The absolute levels of TNF-a in response to IFN-, y/ LPS, though, were less than those observed for the Lewis astrorytes . The Fl astrocyte TNF-a production in response to IFN-y/IIr1O was modest .