Schematic representation of the overall flow of the present study. PEG, polyethylene glycol; HAT, hypoxanthine, aminopterin, and thymidine; IP, immunoprecipitation; MS, mass spectrometry; FCM, flow cytometry. *Mass spectrometry analysis was not performed for the Ab clone U#1 because the antigen was predictable by comparing the protein band detected by immunoprecipitation with U#1 to those detected with mouse monoclonal Abs that we generated previously.