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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

Yersinia pestis capsular antigen Caf1 is shown to be a β-structural protein that in polymeric form possesses very high conformational stability. Different approaches show that a dimer is the minimal cooperative block of Caf1 adhesin. Caf1 dimer interacts effectively with IL-1 receptors of human macrophage and epithelial cells. The specificity of such interaction is confirmed by the inhibition of IL-1α binding by Caf1. The Caf1 role in pneumonic plague pathogenesis is discussed. Keywords: bubonic plague • pneumonic plague • capsular antigen Caf1 • molecular adhesin • conformational stability