A device to simplify the assay of ligand binding to cell surfaces

A sensitive and reproducible technique for characterization of the binding of ¹²⁵I-labeled protein ligands to cell surfaces is described. The physical separation of cell-bound and free ligand was accomplished by centrifugation-filtration using an assembly of plastic micro test tubes. This assembly allowed rapid and efficient separation of free and cell-bound ligands with minimal manipulation of the cells.