In the present study, our data, perhaps for the first time, reveals that high-dose IVIg treatment down-regulates the absolute counts of circulating memory Tfh cells in serious GBS (HFGSs ≧4) patients, which was associated with the decline in the (Tfh2+Tfh17)/Tfh1 ratio along with a decline in serum IL-21 levels. Here, IL21 is linked to Guillain-Barre syndrome.