Demyelination coincides with numerous changes of gene expression in the central nervous system (CNS).Cystatin F (cys F), which is a papain-like lysosomal cysteine proteinase inhibitor that is normally expressed by immune cells and not in the brain, is massively induced in the CNS during acute demyelination.In our previous study, we found that the timing of cys F induction matches the ongoing demyelination and the places with cys F expression overlapped with the remyelinating area, however, the functional role of cys F in demyetinating disease is rather unknown.