Immunihistochemical detection of Bcl-2 in AIDS-associated and classical Kaposi's sarcoma

Kaposi's Sarcoma (KS) is an angioproliferative disease that is characterized by proliferation of spindle-shaped cells predominantly of vascular endothelial cell origin, neoangiogenesis, inflammatory cell infiltration, and edema. Although the lesions of classical KS and AIDS-associated KS (AIDS-KS) share common histological features, AIDS-KS occurs at a markedly higher frequency with a more aggressive clinical course. Immunohistochemical analyses of 26 evolutionarily staged AIDS-KS lesions derived from HIV-infected patients demonstrate significant cytoplasmic levels of Bcl-2, a protooncogene known to prolong cellular viability and to antagonize apoptosis. Bcl-2 expression increases as the pathological stage of KS advances. Immunohistochemical analyses of classical KS lesions demonstrate prevalent expression of Bcl-2 as well, indicating that upregulation of Bcl-2 may be important in the pathogenesis of both classical and AIDS-associated KS. Coexpression of Bcl-2 and factor VIII-related antigen in spindle-shaped cells present within KS lesions suggests that Bcl-2 is upregulated within the vascular endothelial spindle-shaped cells of KS. The consequences of upregulated Bcl-2 expression within KS lesions may be prolonged spindle cell viability which, when coupled with dysregulated cellular proliferation due in part to synergistic activities of inflammatory and angiogenic cytokines and HIV-1 Tat protein, may result in the maintenance, growth, and progression of KS.