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

Measurement of TNF-a Activity. TNF-a activity in culture supernatants was determined in a biologic assay using WEHI 164 clone 13 mouse fibrosarcoma cells as previously described (11) . TNF-cr activity was expressed as TNF-a per culture supernatant (pg/ml). The absolute concentration of TNF-a (pg/ml) was determined by extrapolation from the standard curve, which was generated by using known amounts of human rTNF-a . The lower levels of TNF-a sensitivity in our assay system ranged from 4 to 20 pg TNF-a/ml . All samples were tested in triplicate and are presented as the mean ± SD .