Detection of CD4 on whole blood leukocyte populations derived from an HIV-infected individual (pt 1). The first panel displays the morphologic parameters forward scatter (FSC) and side scatter (SSC) of whole blood leukocyte populations. Three morphologic gates are drawn that encompass lymphocytes (R1), monocytes (R2), and granulocytes (R3). The 3 panels on the right show the fluorescence intensities of each gated population on dual staining with CD4 and CD8 mAbs. The numbers indicate the percentage of positive cells in each quadrant; the quadrant markers are set on the fluorescence intensities of the isotype-matched control mAb within each gate.