SPP1 and glomerulonephritis: In MRLlpr/lpr mice, OPN upregulation begins at the onset of the autoimmune response and positively correlates with the symptom severity [86], which is also influenced by allelic differences in OPN gene [12, 104], since development of glomerulonephritis is favored by the OPN variant carried by MRL strain but not by the one carried by the C3H strain.