Lower levels of S100A12 were associated in patients with a history of lupus nephritis, i.e., “nephritis ever” defined by ACR criteria (median signal of 1591 vs. 1409, with IQR of 613 vs. 583, and Bonferroni-adjusted Mann-Whitney U-test p-value of 0.008) and IRF5 protein levels showed a weak negative correlation to C3a plasma concentration in SLE patients (Spearman's rho = −0.32, p < 0.0001). This evidence concerns the gene S100A12 and systemic lupus erythematosus.