TNFSF13B and immunoglobulin G4-related sclerosing disease: However, as shown in Figure 3b and 3c, no significant correlation was found between the number of affected organs and serum levels of BAFF (n = 13, r = -0.307, P = 0.307) or APRIL (n = 13, r = -0.371, P = 0.212) in patients with IgG4-RD before GC therapy.