Single labeling versus double labeling of cell populations by HLA mAbs. Cells from donor 1 (HLA-A2, A33, B62, B17) were diluted in cells from donor 2 (HLA-A3, A11, B7, B35) in the following percentages: 50, 25, 12.5, 6.25, 3.13, 1.56, 0.78, 0.39, 0.20, 0.098, 0.049, 0.024, 0.012, and 0.006. For single labeling, MCA2090-A647 (anti–HLA-A2) mAb was used. For double labeling, MCA2090-A647 was combined with the mAb BRO11F6-biotine (anti–HLA-A3/A11).