Cell signaling through the PD-1 receptor upon binding the PD-L2 ligａnd attenuates immune responses and is exploited by both tumors and viruses. The PD-L2 Inhibitor Screening Assay Kit is designed for screening and profiling inhibitors of this signaling. The key to this kit is the high sensitivity of detection of biotin-labeled PD-1 by streptavidin-HRP. Only a few simple steps on a microtiter plate are required for the assay. First, PD-L2 is coated on a 96-well plate. Next, PD-1 is incubated with PD-L2 on the plate. Finally, the plate is treated with streptavidin-HRP followed by addition of an HRP substrate to produce chemiluminescence, which can then be measured using a chemiluminescence reader.