Several systems and tissues of relevance for MS may benefit from OPG produced by the placenta; RANK-RANKL-OPG system participates in the regulation of the innate and adaptive immune response, and the elements of the triad are also expressed by microglia, astrocytes, neurons, and oligodendrocyte precursor cells [18,22]. This evidence concerns the gene TNFRSF11B and myeloid sarcoma.