ERBB4 and myeloid sarcoma: We found that the MFI of ErbB4 expression in T cells was lower in RR-MS patients (22.2 ± 3.3) than in HC (37.5 ± 2.4, P = 0.002), the MFI of ErbB4 expression in monocytes was lower in RR-MS patients (88.5 ± 11.5) as compared to HC (135.7 ± 8.9, P = 0.006), and the ErbB4 expression in B cells was lower in RR-MS patients (39.8 ± 4.9) as compared to HC (56.2 ± 3.9, P = 0.018).