Characterization of epitopes on human interleukin-2 using phage displayed-peptide libraries: insights into antibody-peptide interactions.

We have characterized the binding epitopes of two monoclonal antibodies (MAbs) reacting with human Interleukin-2 (IL-2), using a phage display peptide library. The first antibody (CB-IL2.1) recognizes the sequence LSFL, amino acid 72 to amino acid 80, numbered in the IL-2. The second antibody (CB-IL2.2) binds the sequence TTFM (amino acids 101 to 104) located at the opposite site of the four-helix bundle of IL-2. Enzyme-linked immunoadsorbent assay (ELISA) and Western blot using different IL-2 protein construct expressed in bacteria and phage display demonstrate the specificities of this antibody. The data presented here show that the antibodies characterized in this study are raised against linear epitopes and suggest that these epitope are accessible from the outside in the native IL-2 molecule.