The numbers of CCR7−ICOS+ and CCR7+ICOS+ memory Tfh cells and the levels of plasma IL-21 significantly decreased in NMO/NMOSD patients with PR, but not in those with NR, suggesting that intravenous methylprednisolone therapy has a suppressive effect on memory Tfh cells. The gene discussed is IL21; the disease is neuromyelitis optica.