ERVW-1 and myeloid sarcoma: To evaluate the possible interactions between EBV and HERV-W/MSRV/syncytin-1, we focused on cells related to MS pathogenesis and\or target of EBV infection: (i) the astrocytes, that help demyelination, by promoting inflammation, damage of oligodendrocytes and axons, and glial scarring, but also allow remyelination by acting on oligodendrocyte proliferation, and differentiation [62], and (ii) PBMC subsets, that are the main site of EBV replication and persistence, and play pivotal roles in MS in immune defence and immunopathogenesis.