B cells and CD4+ and CD8+ T cells, can play a role in neurodegeneration which is also evidenced by the close association of T cells expressing TNF-related apoptosis-inducing ligand (TRAIL) with dying spinal motor neurons in MS, and alterations in peripheral levels of CD4+ and CD8+ T cells, as observed in AD [48,49]. Here, CD4 is linked to Alzheimer disease.