PDCD1 and immunoglobulin G4-related sclerosing disease: In addition, the frequency of SLAMF7+ population was significantly higher in PD-1+ than PD-1− cTfh1 cells in IgG4-RD patients (14.0 ± 5.59% vs 0.81 ± 0.56%, p < 0.001), suggesting that SLAMF7+ cells are enriched in activated cTfh1 subsets (Fig. 3a).