Flow cytometric analysis of IL-2R and IL-4R expression on tumor cells. Various tumor cells as well as normal C57BL/6 splenic cells were incubated with anti–IL-2R MoAbs (7D4) or anti–IL-4R MoAbs followed by FITC-conjugated secondary Abs as described in Materials and Methods. The cells were analyzed using a flow cytometer. The bold histogram represents the negative control, and the broken histogram shows cells stained for IL-2R or IL-4R expression.