HMOX1 and systemic lupus erythematosus: Given our findings in circulating human monocytes and the interesting results obtained after treating lupus mice with CO, we decided to explore whether HO-1 levels of circulating and infiltrating monocytes play a role in the pathogenesis of human LN, with a special focus on the renal interstitium because it has recently been considered an important predictor of renal outcomes in LN patients (21).