Immunohistochemical and electron microscopic profiles of cutaneous Kaposi's sarcoma and bacillary angiomatosis.

Thirty cases of cutaneous Kaposi's sarcoma (KS) were evaluated and compared with eight cases of acquired immunodeficiency syndrome (AIDS)-related bacillary angiomatosis (BA). The morphologic features of both lesions were studied by light and electron microscopy and by immunohistochemistry with monoclonal endothelial antibodies against CD34, BNH9, and factor VIII-related antigen as well as the lectins Ulex europaeus 1 and Psophocarpus tetragonolobus. Macrophage/monocyte markers used were alpha 1-antitrypsin, lysosome, Kp1 (CD68), and polyclonal factor XIIIa. Electron microscopic studies demonstrated that most of the spindle cells in KS showed a paucity of cell organelles and an absence of Weibel-Palade bodies (WPB), whereas the cells in BA showed activated endothelial cells with WPB. By immunohistochemistry the spindle cells in KS were consistently positive for CD34 only, whereas proliferating cells in BA expressed all endothelial markers used. Numerous cells expressing macrophage/monocyte markers were present surrounding both KS and BA, and a small number of similar cells were entrapped within both lesions. The results demonstrated a restricted immunohistochemical profile for endothelial cell markers in spindle cells of KS (CD34+) distinct from that of endothelial cells in BA. These findings suggest that the spindle cells in KS are poorly differentiated endothelial cells or that they belong to an endothelial cell subset with partial expression of endothelial phenotype.