Expression of Platelet-Derived Growth Factor and Its Receptor in AIDS- Related Kaposi Sarcoma in vivo Suggests Paracrine and Autocrine Mechanisms of Tumor Maintenance

As previously described, proliferation of Kaposi sarcoma (KS)-derived cells in vitro is dependent on the presence of platelet-derived growth factor (PDGF). To test the hypothesis that PDGF may also be a major growth factor for KS cells in vivo, we performed in situ hybridization and immunohistochemical staining for PDGF and PDGF receptors in tissue sections of AIDS-related KS. The data suggest that KS consists of two types of tumor cells. (i) The main population are spindle-shaped cells with elongated nuclei (KS-s cells). They reveal a strong expression of PDGF β receptors but do not express the PDGF-A and PDGF-B isoforms. (ii) A minor population of KS cells express PDGF β receptor as well as PDGF-A and PDGF-B (KS-p cells). These cells are often grouped in whorls and surrounding vascular slits. They reveal spherical nuclei with evenly distributed chromatin and inconspicuous nucleoli. PDGF α receptor is not expressed in either form of KS cells. The results suggest that the isoforms of PDGF and the PDGF β receptor are differentially expressed in two different cell types in KS and that PDGF isoforms may contribute to the pathogenesis of KS.