Multivalent Protein Probes for the Identification and Characterization of Cognate Cellular Ligands for Myeloid Cell Surface Receptors

Cell–cell interactions mediated by cell surface receptor–ligand pairs in the immune system are often of low affinity and transient in nature. To begin to study these weak interactions, it is desirable to devise a generally applicable method for screening for and enriching cells expressing low-affinity ligands for specific cell surface receptors. We describe here an experimental strategy that uses a multivalent form of protein as a probe to identify and characterize cognate ligand(s) of myeloid cell surface receptors. Recombinant fusion proteins containing the receptor protein fragment of interest fused to a truncated Fc domain and a unique biotinylation signal are produced, biotinylated, and coupled to (strep)avidin-coated fluorescent or paramagnetic microspheres. These multivalent microparticle probes are then used to screen or capture cells expressing the cognate cellular ligand(s).