FACS. (A) Primary human Tfh, Teff, and naive T-cell populations were isolated from tonsil via FACS as shown. (B) Intracellular staining for Foxp3 was used to identify the percentage of Tfr cells within the Tfh cell population. Representative flow cytometry plots (left) show the percentages of Foxp3⁺ Tfh or Teff cells in the tonsils using the gating strategy as described in panel A, with data quantified from 5 different patients (right).