A BW reporter system for studying receptor-ligand interactions

Interactions between receptors and ligands constitute a fundamental biological process. However, direct experiments with cells that express the native receptor and the ligand are challenging since the ligand of a specific receptor may be unknown and experimental procedures with the native ligand can be technically complicated. To address these obstacles, we describe a reporter system to detect the binding and activation of a specific receptor by a ligand of interest. In this reporter system, the extracellular domain of a specific receptor is conjugated to mouse CD3ς and this chimeric protein is then expressed in mouse BW cells. These transfected BW cells can then be incubated with different targets (e.g., cells or antibodies). Activation of a transfected receptor leads to the secretion of mouse interleukin-2 (mIL-2) which can be detected by enzymelinked immunosorbent assay (ELISA). This reporter system has the advantages of being sensitive and specific to a single receptor. In addition, the activation level of a specific receptor can easily be quantified and can be used even in cases where the ligand of the receptor is unknown. This system has been implemented successfully in many of our studies to characterize receptor-ligand interactions. We have recently employed this system to study the activation of human Fcγ receptors (FcγRs) by different monoclonal anti-CD20 antibodies in clinical use.