The mouse high affinity IL 2 receptor complex. I. Evidence for a third molecule, the putative gamma-chain, associated with the alpha- and/or beta-chain of the receptor.

Low and high affinity receptors for interleukin 2 were investigated on mitogen-activated mouse T lymphocytes and on interleukin 2 (IL2) receptor-bearing T cell lines by chemical crosslinking of 125I-labelled interleukin 2 (125I IL2) to its binding proteins or membrane proteins associated with the IL2 binding sites. In all cells investigated, the crosslinking produced a 65-70 kD complex thought to be one beta-chain molecule (55 kD IL2 receptor) and one IL2. Occasionally, a 120-130 kD band could be seen which is thought to be IL2 bound to beta-chain homodimer. Using low IL2 concentrations (200 pM), high affinity receptor-bearing cells showed specific additional complexes. Either bands of 85 kD, 105 kD and greater than 160 kD or of 90 kD and 115 kD and greater than 160 kD could be found when mouse T blasts or CTLL 16 cells were used, respectively. In the exclusively low affinity receptor-bearing T cell line Eb, only a single band of 70 kD (beta-chain + IL2) was detectable. These results show that in addition to a 85-90 kD complex, as shown already in humans, a third complex of 105-115 kD exists in mice that is specifically associated with high affinity receptors. This is the first indication of a putative gamma-chain of the high affinity IL2 receptor. All IL2-containing complexes of the mouse cells could be precipitated by the newly developed MAb AMT 45-20 raised against the beta-chain of the mouse IL2R and recognizing an epitope distinct from those recognized by the MAb AMT 13 or IL2. This suggests that either 1) all complexes contain the beta-chain, 2) share an antigenic determinant with the beta-chain, or 3) that the higher mw complexes become coprecipitated with the beta-chain.