Binding of SA/APC to labeled and unlabeled PBL. Method: When used as a second step reagent in Flow cytometry, optimum resolution between signal and background with Ancell biotinylated antibodies was obtained using 20 microl of a 1:10 dilution of the product (or 2 microl of stock) to stain 5 x 10^5 cells. Cells labeled with anti-human MHC Class I/Biotin (#ANC-121-030) stained positive with a 3.1 log shift compared to cells labeled with APC alone.