Distinct Reactivities of Four Monoclonal Antibodies with Human Interleukin 2 Receptor

Two new murine monoclonal IgG1 antibodies, H‐31 and H‐A26, were characterized in comparison with two previously obtained monoclonal antibodies against human interleukin 2 (IL‐2) receptor (IL‐2 R), anti‐Tac and HIEI. In immunofluorescence assays with various human hematopoietic cells, H‐31 and H‐A26 antibodies both reacted with only IL‐2 R‐positive cells, and they precipitated IL‐2 R molecules, glycoproteins with molecular weights of 60K and 53K daltons (gp60/gp53), from human T‐cell leukemia virus type I (HTLV‐I)‐carrying MT‐2 cells, as demonstrated by sequential immunoprecipitation after absorption of IL‐2 R with anti‐Tac. Antibody‐binding competition assays showed that H‐31 and anti‐Tac, and H‐A26 and HIEI, respectively, competed reciprocally in binding to the cells, and that anti‐Tac also inhibited the binding of HIEI but not vice versa . H‐31, like anti‐Tac, strongly inhibited the IL‐2‐dependent proliferation of normal activated T‐cells, absorption of IL‐2 and direct binding of IL‐2 to the cells, while H‐A26, like HIEI, inhibited those processes only weakly. The spectra of reactivities of these antibodies with various simian cell lines derived by HTLV‐I infection were different, as revealed by immunofluorescence studies. Human IL‐2 R was shown to express a unique antigenic determinant, detected with HIEI, that was not detectable in IL‐2 R molecules of Old and New World monkeys, and also to express determinants common to simian IL‐2 R molecules. These observations indicate that H‐31 and H‐A26 recognize human IL‐2 R molecules and that the antigenic sites on the IL‐2 R molecule defined by H‐31, H‐A26, anti‐Tac, and HIEI are different.