A. Representative photomicrographs illustrating double immunofluorescence localization of ErbB1-3 and ErbB2-4 in MCF-7 cells. Localization of ErbB1-3 (red staining) was visualized using monoclonal antibodies with Cy3-conjugated goat anti-mouse IgG (a-f). The same cells were incubated with polyclonal ErbB2-4 antibodies and visualized (green staining) using FITC-conjugated goat anti-rabbit (g-l). Colocalization of ErbB1-3 and ErbB2-4 was determined by merging individual red and green images to give orange-labelled cells (m-r). All receptors are expressed as membrane and cytoplasmic protein. Arrows indicate colocalization at the cell surface. Scale bar = 25 μm. B. Quantitative analysis of MCF-7 cells showing colocalization of ErbB1-3 with ErbB2-4 (for details see legend to Figure 2). C. Quantitative analysis of cells showing ErbB1-3 and ErbB2-4 in distinct locations within the same cell. Data were analyzed as described in Figure 2.