Expression of SIRP on PB and dendritic cells. Mononuclear PB cells were immunolabeled with MoAb P3C4 (IgG2a) and PE-conjugated goat anti-mouse IgG2a-specific antiserum (filled histogram). Nonbinding IgG2a antibody was used as negative control (black line). Cells were analyzed on a FACSCalibur flow cytometer and gated on lymphocytes (LY), monocytes (MO), or granulocytes (GRA); respectively (n = 6). In vitro generated dendritic cells derived from monocytes were labeled with MoAb P3C4 and stained with PE-conjugated goat anti-mouse IgG2a-specific antiserum and anti-CD83–FITC (IgG1). The histogram shows SIRP expression gated on CD83⁺ dendritic cells (n = 3).