The present study demonstrates that basal expression of MSRVenv and syncytin-1 is present in U87-MG astrocytes and in PBMC from MS patients and some healthy donors; among PBMC subsets, MSRVenv and syncytin-1 are expressed by NK, B cells and monocytes, but not by T cells. This evidence concerns the gene ERVW-1 and myeloid sarcoma.