IDENTIFICATION OF A SOLUBLE IL-2 RECEPTOR BETA-CHAIN FROM HUMAN LYMPHOID-CELL LINE CELLS

A clone was isolated from the human lymphoid cell line YT that displayed IL-2R-beta, and was found to express much higher levels of IL-2R-beta than the original cells. Combining cell surface iodination, affinity labeling of the released soluble protein, and fluorescence sandwich-ELISA for both IL-2 and IL-2. (soluble)(s) IL-2R-beta reactants revealed the presence of IL-2-binding protein in the culture supernatant as soluble forms of IL-2R-beta. By using the fluorescence sandwich-ELISA elevated levels of sIL-2R-beta were measured in culture supernatants of human T cell leukemia virus I positive T cell lines. In addition to this constitutive production of sIL-2R-beta, normal PBMC could release low levels of IL-2R-beta by stimulation with PHA. In contrast, this was not found in certain human T cell leukemia virus I negative T cell, B cell and macrophage lines. Immunoprecipitation of the soluble protein with IL-2R-beta-specific mAb characterized it as an apparent 50- to 55-kDa molecule that is distinct from the 45-kDa soluble IL-2R-alpha. Moreover, 10 to 15% of the total cell surface molecules were release into culture supernatants. These results suggest that the released IL-2R-beta might serve as an immunoregulatory function in IL-2 dependent both normal and abnormal immune responses.