Structural and Functional Properties of IL-4δ2, an Alternative Splice Variant of Human IL-4

Structural and functional properties of recombinant IL-4δ2, a naturally occurring splice variant of human IL-4 with a deletion of the loop region 22−37, have been analyzed. IL-4δ2 has α-helical structure and most likely preserves the “up−up−down−down” topology typical of the four-helix-bundle cytokines. IL-4δ2 interacts specifically with the α chain of IL-4R and competes effectively with IL-4 for the common binding sites. Thus, IL-4δ2 may act as a regulator of the cytokine net, being the natural antagonist of IL-4. Keywords: interleukin 4 • interleukine receptor • splice variant • cytokine • four-helix-bundle cytokine