Higher expression of MtF in RARS. Expression of MtF was measured in 5 RARS, 4 RA, and 3 NBM samples. Data are shown as median ± SEM of cells with MtF expression. There were a few MtF⁺ cells in NBM (0%-4%) and RA (median: 3% [0%-8%]) samples during 14-day cultivation. In RARS samples, there was a significant expression of MtF at day 4 (10%), with a continuous increase during the culture period (day 7: 17%; day 11: 13%; day 14: 19%).