Expression of ICAM-1 in implanted primary and metastatic squamous cell carcinomas in rats

F6 tumor cells are derived from a spontaneous rat squamous cell carcinoma (SCC) which originally arose in the facial skin of a DA rat. In this study, FF6 tumor cells were implanted into rat oral mucosa to establish an ex vivo metastatic model. We analyzed the expression of intercellular cell adhesion molecule-1 (ICAM-1) in the implanted primary and metastatic FF6 tumors by immunostaining with a monoclonal antibody (mAb) against ICAM-1. The implanted primary FF6 cells showed strong expression of ICAM-1, whereas the tumor cells of metastatic lesions showed weak or negative expression of ICAM-1. By immunostaining with mAb OX6, a number of MHC class II-positive macrophages were detected in tumor mesenchyme and surrounding the metastatic foci. These results suggested that the local immune reaction in the lymph node influenced the expression of ICAM-1 on tumor cells, and that MHC class II-positive macrophages may play a role in transplanted tumor growth and metastases.