COMPARISON OF THE STRUCTURE OF THE MURINE INTERLEUKIN 2 (IL 2) RECEPTOR ON CYTOTOXIC AND HELPER T CELL LINES BY CHEMICAL CROSS‐LINKING OF 125I‐LABELED IL 2

Abstract

The structure of the murine interleukin 2 receptor (IL2R), on a cytotoxic (CTLL) and a helper (HT2) cell line, has been studied by a combination of chemical cross‐linking with ¹²⁵I‐labeled IL2 and immunoprecipitation with an anti‐receptor monoclonal antibody (7D4). In CTLL cells both methods detected the major 57‐kDa IL2‐binding protein and in addition the cross‐linking studies revealed the presence of a 70–75‐kDa protein associated with the high‐affinity receptor. In the HT2 cell line, however, immunoprecipitation studies revealed three additional proteins of 18, 22 and 37 kDa to the expected 50‐kDa receptor protein. Again cross‐linking studies demonstrated the presence of a 70–75‐kDa protein, which was not immunoprecipitable with the 7D4 antibody. The low molecular polypeptides in HT2 cell were associated with the low‐affinity receptor and represented most likely breakdown products of the 50‐kDa protein. Whereas the 18‐ and 22‐kDa proteins were involved in ligand binding, the 37‐kDa fragment carried the epitope recognized by the 7D4 antibody. Comparative studies with two IL2R antibodies, PC61 and 7D4, revealed that only PC61 inhibited the formation of the IL2 α/β chain complex, although both antibodies reportedly prevent the biological response to IL2. It is speculated that the 37‐kDa fragment, which reacts with the 7D4 antibody, might be involved in IL2 signal transduction. Finally there was no evidence for the existence of a high molecular weight component of the IL2R, previously described as γ chain. In summary, the two‐chain structure of the IL2R has been confirmed for both murine cell lines with some heterogeneity of the α chain. The possibility was raised that a 37‐kDa fragment of the α chain plays a role of in signal transduction.