Fujimi Tanabe

We have recently reported that a novel molecule, murine IFN-gamma-inducing factor (IGIF) produced by mouse liver cells, possesses potent biologic activities, including the induction of IFN-gamma production by spleen cells and the enhancement of NK cell cytotoxicity. In this paper, we report on the isolation of human IGIF cDNA clones from normal human liver cDNA libraries using murine IGIF cDNA as a probe. The amino acid sequence deduced from the human cDNA clones indicated a 193-amino acid precursor peptide and revealed 65% homology with that of murine IGIF. The amino acid sequence of IGIF also included an IL-1 signature-like sequence. Subsequently, the cloned cDNA was expressed in Escherichia coli, and preliminary studies on the biologic activities of the recombinant protein were performed. The recombinant human IGIF induced IFN-gamma production by mitogen-stimulated PBMC and enhanced NK cell cytotoxicity, in a manner similar to murine IGIF. In addition, recombinant human IGIF also augmented granulocyte-macrophage-CSF production and decreased IL-10 production, but had no effect on IL-4 production by Con A-stimulated PBMC. Based on these pleiotropic effects of IGIF, we propose that this novel cytokine be designated as IL-18.

Abstract The novel cytokine interferon‐γ‐inducing factor (IGIF) augments natural killer (NK) cell activity in cultures of human peripheral blood mononuclear cells (PBMC), similarly to the structurally unrelated cytokine interleukin (IL)‐12. IGIF has been found to enhance the production of interferon‐γ (IFN‐γ) and granulocyte/macrophage colony‐stimulating factor (GM‐CSF) while inhibiting the production of IL‐10 in concanavalin A (Con A)‐stimulated PBMC. In this study, when anti‐CD3 monoclonal antibody (mAb)‐stimulated human enriched T cells were exposed to IGIF, the cytokine dose‐dependently enhanced the proliferation of the cells and this could be completely inhibited by a neutralizing antibody against IL‐2 at lower concentrations of IGIF. Neutralizing antibody against IFN‐γ had only insignificant inhibitory effects on T cell proliferation at higher concentrations of IGIF. Enzyme‐linked immunosorbent assays (ELISA) revealed that, like PBMC, T cells exposed to IGIF produced large amounts of IFN‐γ; however, changes in the production of IL‐4 and IL‐10 were minimal. IGIF, but not IL‐12, significantly enhanced IL‐2 and GM‐CSF production in T cell cultures, as determined by CTLL‐2 bioassay and ELISA, respectively; however, both IGIF and IL‐12 enhanced IFN‐γ production by the T cells. When T cells were exposed to a combination of IGIF and IL‐12, a synergistic effect was observed on the production of IFN‐γ, but not on production of IL‐2 and GM‐CSF. In conclusion, IGIF enhances T cell proliferation apparently through an IL‐2‐dependent pathway and enhances Th1 cytokine production in vitro and exhibits synergism when combined with IL‐12 in terms of enhanced IFN‐γ production but not IL‐2 and GM‐CSF production. Based on structural and functional differences from any known cytokines, it was recently proposed that this cytokine be designated interleukin‐18.

Administration of monoclonal anti-CD3 antibody to mice treated with Propionibacterium acnes induced secretion of a high level of gamma interferon (IFN-gamma) into the circulation system, while it induced no significant release in untreated mice. In order to analyze this high-level induction of IFN-gamma in these bacterium-treated mice, we investigated the factors that might be involved. An activity that induces IFN-gamma in T cells was observed in the liver extracts of mice treated with P. acnes and subsequently challenged with lipopolysaccharide. Here, we purified an IFN-gamma-inducing factor from the liver extract to homogeneity and characterized it. Its molecular mass was 18 to 19 kDa, and its pI was 4.9. The amino acid sequence of the NH2-terminal portion was determined and shown to have no similarities to any protein in the EMBL, GenBank, and PIR data bases. The same molecule was also demonstrated in the serum factor that was previously reported to have an IFN-gamma-inducing activity and to have an apparent molecular mass of 75 kDa. Moreover, the activity of this serum factor was recovered in the fraction containing the 18- to 19-kDa protein under reducing conditions and was shown to have the same NH2-terminal amino acid sequence as that of the factor from the liver extract. In addition to the ability to induce IFN-gamma, this protein augmented T-cell proliferation and NK activity in the spleen cells. Thus, several of its biological activities were apparently similar to those of interleukin-12. These results indicated that this novel protein, which exhibited marked costimulatory activity on IFN-gamma production in vitro, was elevated vivo in response to P. acnes treatment. This factor, probably released from the producing cells by lipopolysaccharide stimuli, may be involved in the high-level induction of IFN-gamma in the P. acnes-treated mice.

Glucosyl hesperidin (G-hesperidin) is a water-soluble derivative of hesperidin. We compared the absorption and metabolism of G-hesperidin with those of hesperidin in rats. After oral administration of G-hesperidin or hesperidin to rats, hesperetin was detected in sera hydrolyzed with beta-glucuronidase, but it was not detectable in unhydrolyzed sera. Serum hesperetin was found more rapidly in rats administered G-hesperidin than in those administered hesperidin. The area under the concentration-time curve for hesperetin in the sera of rats administered G-hesperidin was approximately 3.7-fold greater than that of rats administered hesperidin. In the urine of both administration groups, hesperetin and its glucuronide were found. Urinary excretion of metabolites was higher in rats administered G-hesperidin than in those administered hesperidin. These results indicate that G-hesperidin presents the same metabolic profile as hesperidin. Moreover, it was concluded that G-hesperidin is absorbed more rapidly and efficiently than hesperidin, because of its high water solubility.