The ICOSL:ICOS[Biotinylated] Inhibitor Screening Assay Kit is designed for screening and profiling inhibitors of ICOS:ICOSL signaling. The key to this kit is the high sensitivity of detection of biotin-labeled ICOS by streptavidin-HRP. Only a few simple steps on a microtiter plate are required for the assay. First, ICOSL is coated on a 96-well plate. Next, ICOS is incubated with ICOSL on the plate. Finally, the plate is treated with streptavidin-HRP followed by addition of an HRP substrate to produce chemiluminescence, which can be measured using a chemiluminescence reader.