Immunohistochemical detection of multidrug resistance associated P-glycoprotein in tumour and stromal cells of human cancers.

The distribution of Gp 170, a multidrug resistance (MDR) associated glycoprotein, also called P-glycoprotein (P-gp), was examined by immunohistochemistry, using C219 and MRK16 monoclonal antibodies. Sixty-five tumour tissues were studied which included 40 non-lymphoid tumours, 15 chemoresistant non-Hodgkin's lymphomas and 10 Hodgkin's disease. The study was performed on both cryostat and special fixation processed and paraplast embedded (ModAMeX) sections. The latter method preserves fixation-sensitive antigens such as P-gp and allows a more precise morphological identification of neoplastic and non-neoplastic cell populations in contrast to cryostat sections. Immunohistochemical expression of P-gp was expected and confirmed in many non-lymphoid tumours, but stromal macrophages and endothelial cells were also frequently stained in these cases. In non-Hodgkin's lymphomas, cells that were stained with both C219 and MRK16 monoclonal antibodies on cryostat sections were identified as macrophages and endothelial cells and not neoplastic lymphoid cells, by the ModAMeX technique. These findings suggest that the quantitative assessment of MDR RNA by Northern blotting performed on fresh homogenates overestimates the MDR content of neoplastic cells in a number of lymphoid and non-lymphoid tumours. In addition, the mechanism of chemoresistance in non-Hodgkin's lymphomas is less likely to be associated with P-gp expression.