TNFSF13 and systemic lupus erythematosus: However, median serum levels of BAFF in patients with APAP were approximately 32 %, 40 %, and 15 % of those reported in SLE [30], IgG4-related disease [14], and SjS [31], respectively, and those of APRIL were approximately 5 %, 20 %, and 20 % of those in SLE [30], IgG4-related disease [14], and SjS [32], respectively.