Figure 1.

Human innate immune cells contain an intracellular pool of CD33. A, the flow cytometry analysis of CD33 on the cell surface and intracellular in neutrophils (top panel), monocytes (middle panel), and CHME5 cell line (bottom panel). Cells were measured with their membranes intact (green-shaded distributions) and permeabilized using cytoperm/cytofix kit (green-unshaded distributions). IgG controls are in black (intact cells) and gray (permeabilized cells). B, flow cytometry analysis of other CD33rSiglecs in identically treated human neutrophils. The amount of each marker was determined by FACS using the indicated antibodies. Neutrophils were measured with their membranes intact (red-shaded distributions) and permeabilized using cytoperm/cytofix kit (red-unshaded distributions). IgG or secondary antibody controls are in black (intact cells) and gray (permeabilized cells). C, flow cytometry analysis of CD45 in identically treated human neutrophils. Cells were measured with their membranes intact (purple-shaded distributions) and permeabilized using cytoperm/cytofix kit (purple-unshaded distributions). IgG controls are in black (intact cells) and gray (permeabilized cells).