Osteocalcin is an intraosseous protein associated with osteoblasts. Monoclonal antibodies against osteocalcin have about 70% sensitivity and almost total specificity for osteoblastic differentiation. Polyclonal antibodies show cross-reactivity with fibroblasts.
Osteonectin is produced by bone cells but a variety of other cells produce proteins with cross-reacting epitopes, reducing the specificity for osteoblastic differentiation to about 55%, with a sensitivity of about 90%. It is therefore inferior to osteocalcin as a marker of osteoblastic differentiation.
Other putative markers of osteoblastic differentiation have proved disappointing, including bone morphogenetic protein, type I collagen, COL-I-C peptide, decorin, osteopontin, proteoglycans I and II, bone sialoprotein and bone glycoprotein 75.
References
Diagnostic Immunohistochemistry edited by Professor D. J. Dabbs, page 72
This page last revised 21.12.2001.
©SMUHT/PW Bishop