Osteopontin (OPN) is a macrophage chemotactic and adhesion molecule that acts to promote macrophage infiltration in rat antiOsteopontin (OPN) is a highly acidic glycoprotein that contains an adhesive arginine-glycine-aspartic acid sequence.1 OPN functions as a cell adhesion and migration molecule which can bind to a number of ligands including the ␣v␤3 integrin (vitronectin receptor), CD44, collagen type I, and fibronectin.1-3 A wide range of cell types including osteoclasts, some epithelia, macrophages, T cells, smooth muscle cells, and some tumors has been shown to express OPN in a constitutive or inducible fashion.2-9 The adhesive functions of OPN are thought to be involved in diverse biological activities such as bone absorption, tumor metastasis, and inhibition of renal stone formation. 2,9 -11 A functional role for OPN in monocyte infiltration at sites of inflammation has recently been established. OPN, which binds avidly to macrophages, induces prominent monocyte infiltration when injected subcutaneously in mice. 12 In addition, macrophage accumulation induced by intradermal injection of the chemoattractant N-formyl-met-leu-phe in rats is inhibited by administration of a neutralizing anti-OPN antibody. 13Macrophage infiltration is thought to play an important role in mediating renal injury in both immune and nonimmune forms of kidney disease.14 A clear association between up-regulation of OPN expression and macrophage infiltration has been described in a wide range of experimental models of glomerular and interstitial nephritis. [15][16][17][18][19][20][21][22] A functional role for OPN in promoting macrophage-mediated renal injury has recently been demonstrated in rat crescentic anti-glomerular basement

A(2A)R activation suppressed inflammation in the kidneys of MRL/lpr mice and can be considered as a novel therapeutic approach for human lupus nephritis.