Osteopontin is an extracellular matrix cell adhesion protein which is abundant in bone and synthesized by preosteoblasts, osteoblasts and osteoclastic cells that are localized in the mineralized phase of bone matrix. Osteopontin probably exists in tissue-specific isoforms that may correspond to particular cellular functions. Acts as a cytokine it involved in enhancing production of interferon-gamma and interleukin-12 and reducing production of interleukin-11 and is essential in the pathway that leads to type I immunity.

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