Tenascin-C (TN) is an extracellular matrix glycoprotein expressed during embryogenesis. Its distribution is restricted in normal adult tissues and is upregulated in tumors and inflammatory conditions. Twenty-five specimens were studied, including 7 reactive vascular lesions (6 cases of granulation tissue and 1 case of bacillary angiomatosis), and 18 vascular tumors (6 angiosarcomas, 7 hemangioendotheliomas, and 5 AIDS-related nodular type Kaposi's sarcomas). Formalin fixed-paraffin-embedded tissues were stained with monoclonal antibody to TN (DAKO) and with MIB-1 (AMAC). Heterogeneous expression of TN immunoreactivity was seen in all cases, with a diffuse pattern in bacillary angiomatosis and most granulation tissue cases and a focal pattern in angiosarcoma and most hemangioendothelioma cases. Kaposi's sarcoma cases showed both a focal and diffuse pattern of distribution. In most cases proliferation indices (PI) did not correlate with TN expression. Electron microscopy demonstrated active angiogenesis in bacillary angiomatosis and granulation tissue and vasculogenesis in angiosarcoma and hemangioendothelioma. The study demonstrated positive TN expression in reactive lesions with angiogenesis (granulation tissue and bacillary angiomatosis) and neoplastic lesions showing vasculogenesis (angiosarcoma and hemangioendothelioma), although with a different pattern of distribution. These results suggest that TN might be an important extracellular matrix glycoprotein in angiogenesis and vasculogenesis.
Eight cases of cutaneous bacillary angiomatosis related to acquired immunodeficiency syndrome were studied by light and electron microscopy and by immunohistochemistry with a panel of antibodies specific for endothelial and histiocytic markers. Light microscopy showed an inflammatory reaction with florid neovascularization and clusters of Warthin-Starry-positive bacilli. In addition, solid areas of spindle cells were also present that in some cases mimicked Kaposi's sarcoma or other sarcomas. The investigation focused primarily on the spindle cell areas and the angiogenic process present in bacillary angiomatosis. By immunohistochemistry the lesions, including the spindle cell areas, expressed all endothelial markers used; CD34, factor VIII-related antigen, and Ulex europaeus 1 were the most consistent in intensity, however. In those areas the other endothelial markers, BNH9 and Psophocarpus tetragonolobus, were weak and not always uniform. The macrophage/monocyte markers used were alpha 1-antitrypsin, lysosome, kp1 (CD68), and polyclonal factor XIIIa; these revealed a sprinkle of positive cells ranging from 10% to 20% of the cell population. By electron microscopy primitive capillaries were present lined by plump endothelial cells containing frequent abluminal microprocesses forming intercellular lumina. Mitoses and intracytoplasmic lumen formation were infrequent. The study illustrates that bacillary angiomatosis is composed of active endothelial neoformation with the spindle cells representing immature endothelial cells. Furthermore, the features of this angiogenic process recapitulate the morphologic events described in experimental models.
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