TNFRSF11B and myeloid sarcoma: Our findings on sRANKL/OPG ratio in pregnant MS patients and placental OPG production, prompted us to investigate whether the OPG, and in particular, the OPG produced by the placenta could exert its biological activity on maternal cells relevant to the improvement of MS during pregnancy, i.e., astrocytes that could be challenged in the course of MS by the high levels of circulating sRANKL.