TIR-domain-containing adapter-inducing interferon-β (TRIF) is a downstream adaptor of Toll-like receptor (TLR) 4 which is one of the major signal pathways in immune cells leading to neuroinflammtion in central nervous system.The present study was to elucidate the effect of TRIF deficiency on optic nerve (ON) regeneration and retinal ganglion cell (RGC) survival in ON crush model, by means of immunoflurosence, fluro-gold retrograde label, co-culture and real-time PCR (polymerase chain reaction).Using TRIF knock-out (KO) mice, however, no significant regeneration was found in RGC culture.The survival ratio of RGCs was remarkably higher in TRIF KO group when compared with wild type (WT) group in the crush model.We immunostained microglia and found that optic nerve lesion induced more microglial activation in WT group (409 ± 34, per retina) than TRIF-/-group (234 ± 28, per retina).Also in a transwell co-cultured system, WT microglia migrated through the transwell membrane.In contrast, few TRIF-/-microglia did so when performed in in vitro crush model on RGCs.The immediate consequence of inactivation of microglia is reduced production of cytokines like interferon-β (IFN-β).This is supported by our finding that the relative mRNA expression of IFN-β in TRIF-/-group was decreased about 50% than that in WT group and the degenerated function of IFN-β was reduced by IFN-β antibody in a transwell co-culture system.Together, our results indicated that TRIF deficiency promotes axon regeneration in ON via attenuation of microglia activation and consequent reduction in release of harmful cytokines, especially IFN-β.