Monoclonal antibodies which differentiate high- and low-affinity binding sites of interleukin-2

Five monoclonal antibodies (L15, L20, L23, L34, and L61) against human recombinant interleukin-2 were tested for their effects on the interleukin-2 bioactivity and binding. Four of these monoclonal antibodies, L15, L20, L34, and L61, which had neutralizing activity, completely blocked interleukin-2 binding to the high-affinity receptor. On the other hand, L23, which had a very weak neutralizing activity, blocked interleukin-2 binding to the low-affinity receptor. These results suggest that there are at least two distinct binding sites on the interleukin-2 molecule; those for the high-affinity receptor and those for the low-affinity receptor. These monoclonal antibodies should be useful tools in the study of the interaction between interleukin-2 and interleukin-2 receptor.