ICOS and systemic lupus erythematosus: In this study, we found that the proportion of Th2, effector cTfh, PD1+cTfh, and PD1+ICOS+cTfh cells was significantly higher in active SLE patients than in HCs and inactive SLE patients, but these cTfh cell frequencies were not significantly different between inactive SLE patients and HCs, which was consistent with previous studies (20, 21).