Occult expression of CD32 (Fc gamma RII) in normal human peripheral blood mononuclear cells

Three main classes of Fc gamma receptor (Fc gamma R) have been described on the surface of normal human peripheral blood peripheral blood mononuclear cells. These receptors are thought to play an important role in many immune mechanisms. Following interaction with ligand, i.e. IgG in the form of an immune complex, receptor cross-linking occurs and some isoforms of Fc gamma R become internalized and will recycle back to the cell surface. This mechanism may be important in signal transduction pathways. In this study we have shown that a particular type of Fc gamma R (CD32), which is normally expressed on the surface of B cells, can be detected by flow-cytometry within the cytoplasm of up to 90% of normal human peripheral blood lymphocytes. The function of this 'occult' CD32 is not known but may represent an internal receptor pool that is up-regulated following cell activation.