DNAM-1 partially mediates regression of tumor cells in blood. (A) DNAM-1 ligands and ICAM-1 levels on B220^low cells in the blood of preregression, regression, and postregression Eμ-myc mice (bold lines) were compared with WT B220^high cells (dashed line) or isotype control stainings (filled histogram). (B) Analysis of DNAM-1 levels on CD4⁺CD3⁺, CD8⁺CD3⁺ T cells and NK1.1⁺CD3⁻ NK cells from blood of preregression, regression, and postregression Eμ-myc mice (bold lines). Staining was compared with WT NK cells or T cells (dashed line) or isotype controls (filled histogram). (C-D) To determine effector mechanisms of tumor regression in vivo, Eμ-myc mice at 34 days of age were treated with anti–DNAM-1 antibody (100 μg/mouse). Tumor load (C) and B220^low cell number (D) in the blood was determined by flow cytometry at 34, 41, and 48 days of age. The number of B220^low cells in blood (D) was determined as outlined in Figure 1C. Graphs represent the combined data from 2 independent experiments. ctrl, control; d, day.