Poly(I:C) stimulation is not directly toxic to preOLs. A:Western blot analysis of TLR3 expression in astrocyte (AST), oligodendrocytes (OL), and microglia (MG). Splenocytes were used as a positive control. B:Poly(I:C) did not cause cell death in pure preOL cultures. PreOLs were treated with increasing concentrations of poly(I:C) for 48 h and cell viability measured by Alamar blue. Results are combined means ± SEM of 4 independent experiments; ns, not significant. C:Representative phase-contrast images of preOLs treated as above. Scale bar, 100 μm.