IL21 and neuromyelitis optica: We found that the percentages of CCR7− and CCR7−ICOS+ memory Tfh cells were positively correlated with the annual relapse rate (ARR; Figures 6(a) and 6(b)) and with the levels of plasma IL-21 in the NMO/NMOSD patients (Figures 6(c) and 6(d)).