CD40 and peeling skin syndrome: Analysis of MFI revealed that CD40 expression on both regulatory and mature B cells was lower in IgG4-RD patients (14.28 ± 8.91, 12.70 ± 7.14, respectively) compared with those in pSS patients (24.13 ± 6.06; P <0.001 and 26.09 ± 6.90; P <0.001; respectively) and in HC (20.75 ± 5.72; P <0.05 and 23.93 ± 5.86; P <0.001; respectively).