SPP1 Antibody: The secreted protein 1 (SPP1), also known as osteopontin, is a major noncollagenous protein of bone, but is also found in the extracellular matrix of other mineralized tissues and in bodily fluids. In bone, SPP1 is produced by osteoblasts, osteocytes, macrophages, and osteoclasts (1,2). SPP1 binds to cells through integrin and non-integrin receptors, as well as the adhesion receptor CD44 in an RGD-independent manner, enabling SPP1 to induce a number of functional effects including macrophage chemotaxis, cytoprotection, and regulation of T helper type 1 cells (2). SPP1 can regulate biomineralization by inhibiting the formation of hydroxyapatite (3) and the growth of calcium oxalate crystals (4).