TNFRSF1A and primary progressive multiple sclerosis: EAE: Experimental autoimmune encephalomyelitis; DMT-1 : Divalent metal transporter 1; MS: Multiple sclerosis; RRMS: Relapsing-remitting multiple sclerosis; SPMS: Secondary progressive multiple sclerosis; PPMS: Primary progressive multiple sclerosis; BBB: Blood-Brain-Barrier; CNS: Central nervous system; HMC3: human microglial clone 3 cell line; PI: Propidium iodide; t-BHP: tert-Butyl hydroperoxide; ns: not significant; MTT: 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; MOG: Myelin oligodendrocyte glycoprotein; TNF-R1/R2: Tumor necrosis factor receptor 1/2.