Defective M2 macrophages exacerbate the development of SLE by secreting uncontrolled cytokines and promoting the abnormal deposition of immune complexes, such as M2-like macrophages lacking the expression of heme oxygenase-1, which are found in lupus nephritis, a complication of SLE [157]. The gene discussed is HMOX1; the disease is systemic lupus erythematosus.