Identification of functional domains of chicken Interleukin 2

Interleukin 2 (IL-2) is an essential cytokine that plays a pivotal role in the replication, maturation and differentiation of lymphocytes. In this study, the functional domains of chicken IL-2 (chIL-2) were mapped with monoclonal antibodies (mAb), a synthetic peptide, and a phage display peptide library. Nine neutralizing mAbs to chIL-2 were produced using the recombinant chIL-2 monomer expressed in prokaryotic cells as an immunogen and used to finely map the functional domains of the chIL-2 protein. The mimotopes of nine anti-chIL-2 mAbs, including KIELPSL, EHLDXNDSLYL, NHLXGXY, WHLPPSL, EFKASXL, TENPFPE, SGLYL, AHGYWEL and HHGYWEL, were respectively identified by phage display and peptide-competitive ELISA. These mimotopes constitute three conformational functional domains in the chIL-2 molecule, that is, N26K27I28H29L30E31L32P35Q43Q44T45L46Q47C48Y49L50 (domain I), E68E69F70K79K82S83L84T85G86L87 (domain II) and N88H89G91K104F105P106D107E111L112Y118L119 (domain III). The neutralizing mAbs to chIL-2 inhibited the in vitro lymphocyte proliferation stimulated by three peptide domains of chIL-2. The predicted tertiary structure of chIL-2 reveals that domain I was positioned in the long A–B loop and the N terminal of Helix B, domain II was mostly situated in Helix C, and domain III was distributed in the C–D loop and Helix D. These data demonstrate the functional domains of chIL-2 and provide a clue for elucidating the interaction between chIL-2 and its receptor.