CD40 and immunoglobulin G4-related sclerosing disease: We evaluated CD40 expression in IgG4-RD, pSS and HC; the results not only revealed that in IgG4-RD patients CD19+ B lymphocytes expressed a lower frequency of CD40, but that decreased MFI of CD40 was also found in all B-cell subsets including regulatory, memory, and mature B cells from IgG4-RD patients.