Conversion of low-affinity interleukin 2 receptors to a high-affinity state following fusion of cell membranes.

The cellular receptors for interleukin 2 (IL-2) exist in at least two forms, one with a particularly high affinity and a second, more numerous class, with a much lower affinity for IL-2. Indirect evidence suggests that both classes of receptors use the same p55 glycoprotein as their ligand-binding component. L cells transfected with cDNA encoding this protein, however, displayed only low-affinity IL-2 binding. To determine if such receptors could be converted to a high-affinity state, L-cell membranes containing the murine p55 protein were fused with membranes from human T cells displaying high-affinity receptors. The anti-Tac antibody was used to block ligand binding to human p55 on the fusion product. The results showed that a fraction of the murine p55 chains were converted to a dramatically higher affinity following fusion. Fusion of the L-cell membranes with themselves or with membrane preparations from human T-cell lines lacking the IL-2 receptor resulted in little or no affinity modulation. One explanation of the results is that cofactors present in receptor-positive T-cell lines crossed species lines and combined with the murine p55 chain to create "high-affinity" binding sites. Thus, depending upon its environment, the same p55 molecule can apparently form either a low- or high-affinity IL-2 receptor.