Staining of isolated PMN with affinity purified phage clones and analysis by flow cytometry. PMN were incubated with affinity purified phage clones or irrelevant control phage followed by biotinylated anti-phage antibody and labeled with FITC conjugated to streptavidin. The distinct staining pattern of the analyzed phage suggests binding to different target molecules. All phage clones, but not the control phage, showed brighter signals by incubation at 20°C. The DLVTSKLQV displaying phage (or other homologous phage, data not shown) consistently labeled approximately 50% of the cells. Incubation of cells with the CKDGLFLGSWLC-displaying phage at 4°C resulted in staining of a small cell subpopulation that could be identified as monocytes on the orthogonal light scatter (data not shown) but not in labeling of the main cell population consisting of PMN. Histograms represent specifically stained cell numbers on the vertical axis (labeled counts) plotted against fluorescence on a log scale from 5,000 cells per condition. These results were obtained in four separate analyses.