Dose-dependent binding of ab168048. Recombinant Human TNFSF9 saturates its receptor at a concentration range of 2-4000ng/ml. Method: Receptor binding assay: a 96-well ELISA plate was coated O/N with 50ng per well of CD137 (Human):Fc (Human) (rec.) (4-1BB:Fc). After a blocking step, the indicated concentrations of ab168048 were added for 1 hour. After extensive washing, an Enhancer was added for 1 hour. Bound ligand was revealed by a rabbit anti-mouse IgG-HRP (1/1000 dilution) incubated for 1 hour. OPD was used as a substrate and absorbance was measured at 490nm in an ELISA reader.