The high affinity interleukin 2 receptor: evidence for three distinct polypeptide chains comprising the high affinity...

Low and high affinity receptors for interleukin 2 were investigated on interleukin 2 (IL-2) receptor bearing cells by chemical cross-linking of 125I-labelled IL-2 to its receptor, or membrane proteins associated with the IL-2 binding sites. SDS-PAGE analysis of the cross-linked complexes of the murine CTLL 16 cells and human T-blasts, which bear high and low affinity IL-2 receptors, showed three distinct bands. The fastest of those three bands ran in parallel to the single band of 65-70 kDa found on the only low affinity receptor bearing mouse T-lymphoma Eb, which is thought to be one beta-chain (55 kDa IL-2 binding protein) and one IL-2. Both upper bands ran in parallel with those produced by the 2C8 clone of the NK-like cell line YT which lacks the 55 kDa binding protein and bears only a single class of receptors with an intermediate affinity. Internalisation studies using CTLL 16 cells revealed that all three bands disappeared under conditions allowing receptor internalisation. Low and high affinity binding sites of CTLL 16 cells were destroyed by trypsinisation and the IL-2 binding properties of the cells were regenerated in parallel with the reappearance of all bands. These results show in addition to the beta-chain (55 kDa binding protein) and the alpha-chain 75 kDa binding protein, an IL-2 membrane protein complex with an apparent mol. wt of 115 kDa in CTLL 16 cells. They are the first direct indication of a putative gamma-chain of the high affinity IL-2 receptor.