Considering previous findings reporting the number of Tr1 cells was decreased, and the activity of Tr1 cells for secreting IL‐10 was also impaired in MS patients, MS monkeys, and mouse EAE model by multiple mechanisms (Astier & Hafler, 2007; Ma et al., 2009; Martinez‐Forero et al., 2008), we found both Tr1 and Treg cells decreased in NMOSD patients. Here, IL10 is linked to myeloid sarcoma.