Intermolecular cystine-bonding of murine interleukin 2 indicates that ligand dimerization is important for the formation of the high-affinity receptor complex

Four Cysteine Residues Contribute to Homodimerization of Chicken Interleukin-2

Interleukin-2 (IL-2) is a pleiotropic cytokine regulating the immune and nervous systems. Mammalian and bird IL-2s have different protein sequences, but perform similar functions. In the current study, two bands were detected by immunoblotting using an antibody against freshly purified chicken IL-2 (chIL-2). The molecular weight of the larger band was approximately twice as much of the chIL-2 monomer, although a chIL-2 complex or homodimer has never been reported. To explain this intriguing result, several dissociation reagents were used to examine the intermolecular forces between components of the proposed chIL-2 complex. It was found that intermolecular disulphide bond promotes homodimerization of chIL-2. Subsequently, mutation of Cys residues of chIL-2 revealed that mutation of all four Cys residues disrupted homodimerization, but a single, dual, or triple Cys mutation failed to disrupt homodimerization, suggesting that all four Cys residues on chIL-2 contribute to this dimerization. Functional analysis showed that both monomeric and dimeric chIL-2 consisting of either wild type or mutant chIL-2 were able to stimulate the expansion of CD4⁺ T cell in vivo or in vitro, and effectively bind to chIL-2 receptor. Overall, this study revealed that the recombinant chIL-2 purified from either Escherichia coli (E. coli) or Spodoptera frugiperda (Sf9) cells could homodimerize in vitro, with all four Cys residues on each chIL-2 protein contributing to this homodimerization, and dimerization and Cys mutation not impacting chIL-2 induced stimulation of chicken CD4⁺ T cells.

Interleukin-10 inhibits antimicrobial activity against Leishmania major in murine macrophages

The stimulation of macrophages is of importance to the defense against intracellularly replicating microorganisms such as Leishmania. In this study the direct effect of recombinant interleukin-10 (IL-10) on the leishmanicidal effector functions of murine peritoneal or bone marrow derived macrophages was investigated. IL-10 almost completely inhibited the killing of intracellular leishmania at concentrations above 10 ng/ml. This inhibitory effect was independent of the stimulus used as the activation of macrophages by IFN-gamma and IL-7, recently shown to possess macrophage activating properties, were suppressed by IL-10. Kinetic experiments revealed that IL-10 must be present during the process of macrophage activation and that the leishmanicidal effector function of fully activated macrophages was not influenced. Furthermore, in the absence of exogenously added IL-10, the addition of neutralizing antibodies against IL-10 or IL-10-specific antisense phosphorothioate DNA-oligonucleotide led to an enhanced killing of parasites after stimulation with either IFN-gamma or IL-7. In accordance with this, IL-10 mRNA was readily detectable in murine macrophages by PCR with reverse transcribed mRNA. These results indicate that IL-10, which is endogenously produced by macrophages, acts as an autocrine deactivating factor supporting the survival of the parasite.

Homodimeric murine interleukin-3 agonists indicate that ligand dimerization is important for high-affinity receptor complex formation

Homodimeric murine interleukin 3 (mIL-3) agonists were generated by intermolecular cystine-bonding. Steady-state binding assays and association kinetics performed at 4 degrees C using these agonists revealed specific binding to both the high- and low-affinity receptor. DSS-mediated crosslinking studies performed at 4 degrees C with agonist concentrations compatible with high-affinity receptor complex formation allowed to detect protein complexes of the alpha chain, the beta chain(s) and the high-affinity receptor complex migrating with apparent molecular weights of 90 kDa, 140 kDa, and above 180 kDa, respectively. In contrast, monomeric mIL-3 was crosslinked to the alpha chain receptor only unless high concentrations were used. Binding studies performed at 4 degrees C revealed a positive cooperative interaction of monomeric mIL-3 with the low-affinity receptor. Proliferation studies and association kinetics performed at 37 degrees C showed that under physiological conditions these agonists were at least 2- to 3-fold more potent than monomeric mIL-3. We therefore propose that dimerization of mIL-3 may be involved in high-affinity receptor complex formation.