Quantitation of cellular receptors by a new immunocytochemical flow cytometry technique

Flow cytometry provides a rapid qualitative method for analyzing the binding of a fluorescent probe to a cell. To quantitate the binding of a probe using flow cytometry, one must be able to first calibrate the fluorescent signal with some known standard. We have compared a new one-step method with a previous two-step method for determining the number of binding sites (receptors) on the surface of cells using immunofluorescent staining of the cells and analysis by flow cytometry. Experimentally, recombinant chinese hamster ovary cells, expressing cell surface glycoprotein receptors, IIb/IIIa or Mac-1, were assayed using specific mouse monoclonal antibodies against these receptors. The two methods yielded comparable results and, depending on the cell type, detected anywhere from 100,000 to 300,000 antibody-binding sites per cell, respectively.