MELANOCYTES FRESHLY ISOLATED FROM NORMAL HUMAN SKIN EXPRESS THE CELL-MEMBRANE RECEPTOR FOR THE ADHESIVE GLYCOPROTEIN THROMBOSPONDIN

Thrombospondin (TSP) is an adhesive protein with multiple binding site s, which is able to mediate several cell-to-cell and cell-to-matrix in teractions, particularly through its cell membrane receptor (TSP-R). B ecause human keratinocytes are able to synthesize and express TSP, and as TSP is also localized at the dermal-epidermal junction in normal h uman skin, we questioned whether epidermal cells are able to bind avai lable TSP, that is, to express TSP-R. To investigate this, we employed gold immunoelectron microscopy on epidermal cells freshly isolated fr om normal human skin; the TSP-R was detected by OKM5 monoclonal antibo dy. Epidermal cells showing ultrastructural characteristics of melanoc ytes were gold-stained on their plasma membrane, whereas keratinocytes , Langerhans cells and lymphocytes were unstained. Although functional studies are clearly necessary to clarify the role(s) played by the TS P-R on the cell surface of melanocytes, it is tempting to speculate th at the TSP-R may be important for melanocyte adhesion to the dermal-ep idermal junction and to keratinocytes. Such adhesion may not only subs erve the steric localization of melanocytes, but also have important i mplications for those functional activities of melanocytes which have been shown to require close contact between these cells and adjacent k eratinocytes and/or basement membrane components.