There was no statistical difference in total serum IgG levels between IgG4-RD (24.58 ± 10.74 g/L) and pSS patients (22.99 ± 11.48 g/L; P >0.05); however, the serum IgA and IgM levels in IgG4-RD patients (1.85 ± 0.76 g/L, 0.82 ± 0.38 g/L, respectively) were significantly lower compared with those in pSS patients (4.17 ± 2.23 g/L; P <0.001 and 1.24 ± 0.64 g/L; P = 0.001). This evidence concerns the gene CD40LG and immunoglobulin G4-related sclerosing disease.