CD56 and CD8 population subsets in human peripheral blood. (A) Six subsets were identified in human T cells by staining with CD56 and CD8. Gating and subsequent identification are indicated in the figure for population frequencies after IL-2 treatment. (B) IL-2–activated PBMCs (200 ng/mL, 12 hours) were mock-treated (IgG) or treated with ICAM-1, ICAM-2, or ICAM-3 (10 μg/mL FC fusion protein) 30 minutes prior to incubation with target HL60 cells at a 1:50 E/T ratio for 4 hours. Cells were then prepared for flow cytometry with CD8-Cy5PE, CD56-PE surface stains and perforin-Cy5 intracellular stains. Cells were gated in perforin content low, medium, and high, and then subsequently analyzed for CD56 and CD8 expression. Panel on the left is in the absence of target cells and panels on the right are in the presence of target cells. Numbers in panels correspond to population frequencies in those gates.