According to the rs2221903 polymorphism, SLE carriers of the CT genotype showed higher IL-21 levels [120.7 pg/mL (IQR 99.8–166.9)] than carriers of the TT genotype [107.8 ng/mL (91.6–130.5)] with a statistical difference (p = 0.0236, Figure 3a). This evidence concerns the gene IL21 and systemic lupus erythematosus.