However, several studies have shown that an elevated frequency of cTfh1 cells is observed in active SLE patients, and that an increase in ICOS+PD-1+cTfh1 cell population is correlated with the number of plasmablasts and high-affinity antibody production in humans after influenza vaccines (22, 33, 34). Here, PDCD1 is linked to systemic lupus erythematosus.