AIDS-related Kaposi's sarcoma displays differential expression of endothelial surface antigens

The authors studied 11 cases of Kaposi's sarcoma (KS) in patients with the acquired immunodeficiency syndrome (AIDS) for their reactivity with two monoclonal antibodies (B721 and E431) that recognize endothelial cell surface antigens. Reactivity of these antibodies with KS was compared with the reactivity of other known endothelial markers (F8rAg, Ia, HCL-1). Staining was done with avidin-biotin-alkaline phosphatase immunohistochemistry on acetone-fixed frozen sections. In all samples of tumor both the spindle cell component and the vascular lining cells stained with both B721 and E431. In general, the spindle cells stained less intensely than did the vascular lining cells. There was both intratumor and intertumor variability. B721 and E431 are proposed as two additional markers for KS, and it is suggested that their reactivity with the tumor supports the hypothesis that KS is derived from vascular endothelium. The possibility is also raised that the variability of staining for vascular markers could have diagnostic possibilities, and further studies for investigation of this hypothesis are suggested.