Flow cytometric demonstration of shared antigens between human bladder cancer cells and normal host macrophages

Leukocyte infiltration has been studied with flow cytometry in a series of 76 bladder tumors. Cell DNA content and surface immunofluorescence with a panel of 6 monoclonal antibodies (Mabs) were evaluated using a double-staining technique. The following Mabs were used: anti-CD5 (ST1); anti-CD37 (SB3); anti-granulocytes (WEMG1); anti-monocytes/macrophages (PHM2); a Mab directed against a bladder tumor-associated antigen (G4), and the anti-keratin-18 RGE53. Antigens recognized by Mabs ST1, SB3 and WEMG1, were only expressed by cells with a DNA index close to 1, whatever the grade or the DNA profile of the tumor. Conversely, PHM2 was not only expressed by cells with a DNA index close to 1, but also by cells with a DNA index of more than 1.5, i.e., by cells of the second peak in tumors with a bimodal DNA profile. Thus the PHM2 epitope was not exclusively expressed by macrophages but also by urothelial tumor cells with an elevated DNA index. A significant positive correlation (r = 0.87; p less than 0.01) was found between DNA index and PHM2 reactivity among cells of the second peak in tumors with a bimodal DNA profile, whereas there was no correlation between DNA index and cytokeratin-18 expression and a weak negative correlation (r = -0.42; p less than 0.02) between DNA index and G4 Mab reactivity. These findings support the hypothesis of a cell fusion between human malignant urothelial cells and normal host macrophages.