Background and design: Historically, the Kaposi's sarcoma (KS) tumor cell was generally thought to be derived from endothelial cells. However, by immunohistochemical staining of lesions, many spindle-shaped cells in KS express factor XIIIa, suggesting that they may be related to dermal dendrocytes, a perivascular cell of monocyte/macrophage lineage. To extend our observations on tissue sections of lesions, four different established KS-derived cell lines before and after cytokine exposure, as well as biopsy specimens of KS lesions, were studied for the expression of endothelial cell and monocyte/macrophage antigens.
Results: Multipassaged KS tumor cells grew predominantly as spindle-shaped cells. By immunohistochemical staining, all four KS-derived cell cultures were factor XIIIa and intercellular adhesion molecule 1 positive. Three KS-derived cell cultures were CD14 and vascular cell adhesion molecule 1 positive. Expression of factor XIIIa was upregulated by interferon gamma. By polymerase chain reaction (PCR) analysis, expression of CD4 mRNA was also detected in all four KS-derived cell cultures. Expression of these monocyte/macrophage markers (factor XIIIa, CD14, and vascular cell adhesion molecule 1) on KS in vitro was also detected on spindle cells of KS lesions in vivo. Endothelial leukocyte adhesion molecule 1 and factor VIII expression was not detected on KS-derived cells in vitro before or after exposure to interferon gamma or tumor necrosis factor alpha. While cultured KS cells strongly expressed smooth-muscle alpha-actin, no detection was observed on spindle-shaped cells in vivo. Conversely, while cultured KS cells were devoid of CD34, the tissue biopsy specimens contain strongly positive spindle-shaped cells. Our results demonstrate that while KS cell lines express one antigen shared by endothelial cells, ie, vascular cell adhesion molecule 1, they lack several other endothelial cell markers such as factor VIII and endothelial leukocyte adhesion molecule 1, either before or after cytokine activation.
Conclusions: Kaposi's sarcoma cell lines express several antigens linking them to dermal dendrocytes such as factor XIIIa, CD4, and CD14.