Thirty-three cases of European Kaposi's sarcoma (KS) were investigated by immunohistochemical methods using a panel of antibodies specific for the markers of the cell types proposed for its histogenesis in the literature: S-100 protein for Schwann cells; lysozyme for histiocytes; alpha-actin, desmin and vimentin for pericytes and other mesenchyme-derived cells; factor VIIIR:Ag and Ulex europaeus agglutinin-I for endothelial cells. Antifibronectin antibodies were also used in order to investigate some functional activities of the proliferating cells. Immunohistochemical results showed that KS cells were diffusely positive for vimentin and alpha-actin and negative for all other cell markers. Furthermore, KS cells were constantly surrounded by fibronectin-positive material. Since the KS cells are diffusely positive for vimentin, they may be considered a monotypic proliferation of mesenchyme-derived cells which lack the markers of full endothelial cell differentiation; however, the occurrence of fibronectin-positive material around them suggests that these cells are actively proliferating endothelial cells and their diffuse positivity for alpha-actin suggests a possible differentiation to pericytic cells. In conclusion KS cells may be considered as mesenchymal cells which are at an intermediate stage of maturity or immaturity in vascular differentiation.
