The immunohistochemical expression profile of osteopontin in normal human tissues using two site-specific antibodies reveals a wide distribution of positive cells and extensive expression in the central and peripheral nervous systems

To elucidate the cellular distribution of osteopontin (OPN) in normal human tissues, we undertook immunohistochemistry using two site-specific OPN antibodies. The 10A16 monoclonal antibody was raised against the amino acid sequence just downstream of the thrombin cleavage site, while the O-17 polyclonal antibody was raised against the N-terminal peptide. Each antibody has been confirmed previously to react with both whole OPN and its relevant fragments. The expression pattern for these two antibodies was similar in distribution. In addition, we also identified expression in Ebner's gland, type II pneumocytes, Kupffer cells, cells of the endocrine organs, anterior lens capsule and ciliary body, synovial type A cells, mesothelia, adipocytes, and mast cells. Neurons and glia in the central nervous system and spinal cord, cranial and peripheral nerve sheaths, ganglion cells in the sympathetic ganglion, intestinal plexuses, retina, and choroid plexus also regularly exhibited OPN positivity. Testicular germ cells, pancreatic exocrine cells, and follicular dendritic cells reacted with 10A16 only, whereas lutein cells and taste bud cells exhibited O-17 reactivity alone. These minor differences were hypothesized to reflect the state of OPN in the cells; that is, whether OPN was in its whole molecule or fragmented form. In conclusion, we demonstrate that OPN is widely distributed in normal human cells, particularly those comprising the central and peripheral nervous systems.