Evidence for capping of Fcγ receptors on osteoclasts

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Abstract
Fc receptors, cell surface structures which bind the Fc portion of immunoglobulins, facilitate endocytosis and mediate triggered enzyme release in the phagocytic cells of the mononuclear phagocyte system (MPS). The osteoclast and the macrophage share many similarities, and it has been suggested that they are both derived from a common MPS precursor cell. Nevertheless, Fcγ receptors, found on both primitive and well-differentiated cells of the mononuclear phagocyte system, have yet to be demonstrated on the osteoclast cell membrane. The aim of the present study was first, to study the distribution of rat endogenous IgG around resorbing bone using immunohistochemistry and the avidin-biotin-peroxidase (ABC) technique; and second, to determine if rat osteoclasts express Fcγ receptors, using a recently described technique based on the ABC method. Observations that endogenous IgG accumulated at osteoclast/bone interfaces, and that Fcγ receptors, expressed by osteoclasts, “capped” in the same area, have important implications regarding the origin of this cell and its mechanisms of bone attachment and resorption.