Osteopontin for instance, although increased in SLE patients in other studies and associated with disease activity and specific clinical manifestations35,36 was in our study mostly expressed in inactive SLE patients, which was rather unexpected, considering its role as an inflammation marker.37 A recent small study found OPN expressed at higher levels in urine than in the serum of SLE patient, with the serum protein being a possible marker of LN presence, but unable to correlate with the phase of renal activity.18 Here, SPP1 is linked to systemic lupus erythematosus.