Flow cytometry of m909 IgG on FRβ-positive cells. hFRβ-positive cells were incubated with 0.001, 0.01, 0.1, 1, 10, and 100 nM m909 IgG. An isotype control IgG1 was included in the test at 100 nM. Cells were analyzed in FACSCalibur. (a) CHO-hFRβ cells. (b) PreB L1.2 cells. Black line indicates isotype control IgG, and colored lines indicate 0.001 to 100 nM m909. (c) CHO-hFRβ cells were incubated with 10 nM folate-FITC (green line) and 10, 100, and 1,000 nM unlabelled m909 (other colored lines). (d) CHO-hFRβ cells were incubated with 10 nM folate-FITC and varying concentrations of m909-FITC. Binding of m909 and folate did not interfere with each other. Black line indicates negative control, green line indicates FITC-folate alone, and other colored lines indicate FITC-folate with 0.1, 1, 10, or 100 nM m909-FITC. FITC, fluorescein isothiocyanate; FRβ, folate receptor beta; hFRβ, human folate receptor beta.