Expression of endothelial cell markers PAL-E and EN-4 and Ia-antigens in Kaposi's sarcoma

Eleven biopsy specimens of Kaposi's sarcoma (KS) removed from the skin and oral mucosa were examined immunohistochemically with monoclonal antibodies PAL-E and EN-4, specific for human vascular endothelial cells, and with LN-3 monoclonal antibody reactive with immune-associated (Ia) antigens in the HLA-DR locus. The early lesions of KS, corresponding to the patch phase, contained hyperplastic venules and an increased number of lymphatic capillaries. The lymphatic capillary endothelium was reactive with EN-4, whereas, PAL-E reacted only with blood vessel endothelial cells. The spindle cells, like lymphatic endothelial cells, were non-reactive with PAL-E but showed positive reaction with EN-4 antibodies. The observed morphologic pattern of vasculogenesis and the demonstrated immune-reactivity in KS support an origin from the venule-lymphatic junction. This is an aberrant pattern but reminiscent of normal embryonal lymphatic channel development. The lymphatic capillaries and vascular slits were nonreactive with LN-3 antibody, but it was positive on cell membranes in a number of spindle cells, suggesting the focal expression of Ia-antigens.