Osteopontin: another piece in the systemic lupus erythematosus immunopathology puzzle.

Osteopontin (OPN) is a phosphoglycoprotein involved in bone remodelling, wound healing, cell adhesion, tissue remodelling, and immune response that is distributed widely in normal adult tissues. OPN biological activity is regulated by thrombin and matrix metalloproteinases (MMPs) cleavage, where the full-length (OPN-FL) protein and the cleaved OPN-N are associated with autoimmune diseases such as systemic lupus erythematosus (SLE). OPN overexpression has been associated with a predisposition to SLE and bad prognosis since OPN could mediate a sustained polyclonal B cell activation that besides to intracellular OPN (iOPN) form, promote the T follicular helper (TFH) cells and enhance anti-nuclear antibody production. Currently, the role of OPN in lupus nephritis (LN) has been reported and extensively studied; however, no data are available about the potential mechanism of OPN in neuropsychiatric SLE (NPSLE). In this review, we highlighted the contribution of OPN and iOPN in LN and NPSLE immunopathology.