CD40 and peeling skin syndrome: Both the percentage and the MFI of CD40 on CD19+ B lymphocytes were lower in IgG4-RD patients (44.35 ± 21.79%, 12.32 ± 6.28, respectively) compared with those in pSS patients (69.48 ± 20.33%; P <0.001 and 21.47 ± 8.23; P <0.001; respectively) and in HC (87.08 ± 11.27%; P < 0.001 and 27.32 ± 6.13; P <0.001; respectively; Figure 2I-J).