An immunohistological study of factor VIII related antigen and Kaposi's sarcoma using polyclonal and monoclonal...

Immunohistochemical techniques have been used to demonstrate Factor VIII related antigen (FVIIIRA) in endothelial cells and to study a variety of tumours including Kaposi's sarcoma. Conflicting reports on the presence of this antigen within the spindle cells of Kaposi's sarcoma have been made. These differences may be due to variations in techniques, in the immunoreagents used and in the method of fixation and handling of the specimen. A major factor may also be the lack of a uniform interpretation of positive peroxidase labelling. This study was confined to paraffin-embedded tissues and compared the results and distribution of FVIIIRA labelling in Kaposi's sarcoma using two commercially available polyclonal antibodies and three monoclonal antibodies. The effects of predigesting the sections with trypsin and protease were also evaluated. Positive labelling of tumour spindle cells was accepted only when it matched that seen in labelled endothelial cells. The polyclonal antibodies provided satisfactory localization of FVIIIRA and gave positive results more frequently than the monoclonal antibodies both with and without enzyme digestion. Endothelial labelling was evident in vessels both within and around the tumour but none was seen in the tumour spindle cells. Most previous studies gave no definition of positive labelling but spindle cells were reported as labelled. However, in those few reports where a definition was given the findings are analogous to those in this report, demonstrating the importance of defining positive labelling.