Interleukin-18 and host defense against infectious pathogens

Differential Inhibition of Inducible T Cell Cytokine Secretion by Potent Iron Chelators

Effector functions and proliferation of T helper (Th) cells are influenced by cytokines in the environment. Th1 cells respond to a synergistic effect of interleukin-12 (IL-12) and interleukin-18 (IL-18) to secrete interferon-gamma (IFN-γ). In contrast, Th2 cells respond to interleukin-4 (IL-4) to secrete IL-4, interleukin-13 (IL-13), interleukin-5 (IL-5), and interleukin-10 (IL-10). The authors were interested in identifying nonpeptide inhibitors of the Th1 response selective for the IL-12/IL-18-mediated secretion of IFN-γ while leaving the IL-4-mediated Th2 cytokine secretion relatively intact. The authors established a screening protocol using human peripheral blood mononuclear cells (PBMCs) and identified the hydrazino anthranilate compound 1 as a potent inhibitor of IL-12/IL-18-mediated IFN-γ secretion from CD3+ cells with an IC50 around 200 nM. The inhibitor was specific because it had virtually no effect on IL-4-mediated IL-13 release from the same population of cells. Further work established that compound 1 was a potent intracellular iron chelator that inhibited both IL-12/IL-18- and IL-4-mediated T cell proliferation. Iron chelation affects multiple cellular pathways in T cells. Thus, the IL-12/IL-18-mediated proliferation and IFN-γ secretion are very sensitive to intracellular iron concentration. However, the IL-4-mediated IL-13 secretion does not correlate with proliferation and is partially resistant to potent iron chelation

Association between interleukin-18 gene polymorphism and Helicobacter pylori infection in the Korean population

Interleukin-18 (IL-18) is a pleiotropic, pro-inflammatory cytokine that is capable of promoting the Th1 response. A predominant Th1 response induces chronic and persistent inflammatory changes in the gastric mucosa in response to Helicobacter pylori (H. pylori) infection. The aim of this study was to investigate the potential association between IL-18 gene polymorphisms and susceptibility to H. pylori infection in the Korean population. A total of 678 subjects who underwent a routine health check-up were enrolled. The IL-18 gene polymorphisms at positions −656, −607, −137, +113, and +127 were genotyped. H. pylori positivity was demonstrated in 456 subjects (67.3%). The allele frequencies of IL-18 gene polymorphisms at position −137 (rs187238) were different based on the status of H. pylori infection (G vs. C, adjusted OR 0.64 CI: 0.47–0.87, P = 0.005). The results indicate that the genetic variants in the IL-18 gene may be associated with susceptibility to H. pylori infection in the Korean population, suggesting that IL-18 plays a role in the pathogenesis of H. pylori-associated diseases. However, this finding requires further replication and validation.

Acapsular Cryptococcus neoformans activates the NLRP3 inflammasome

Cryptococcus neoformans (C. neoformans) is an opportunistic fungal pathogen that mainly infects immunocompromised individuals such as AIDS patients. Although cell surface receptors for recognition of C. neoformans have been studies intensively, cytoplasmic recognition of this pathogen remains unclear. As an important detector of pathogen infection, inflammasome can sense and get activated by infection of various pathogens, including pathogenic fungi such as Candida albicans and Aspergillus fumigatus. Our present study showed that acapsular C. neoformans (cap59Δ) activated the NLRP3-, but not AIM2-nor NLRC4- inflammasome. During this process, viability of the fungus was required. Moreover, our in vivo results showed that during the pulmonary infection of cap59Δ, immune cell infiltration into the lung and effective clearance of the fungus were both dependent on the presence of NLRP3 inflammasome. In summary, our data suggest that the capsule of C. neoformans prevents recognition of the fungus by host NLRP3 inflammasome and indicate that manipulation of inflammasome activity maybe a novel approach to control C. neoformans infection.

Interleukin 18 in the CNS

Interleukin (IL)-18 is a cytokine isolated as an important modulator of immune responses and subsequently shown to be pleiotropic. IL-18 and its receptors are expressed in the central nervous system (CNS) where they participate in neuroinflammatory/neurodegenerative processes but also influence homeostasis and behavior. Work on IL-18 null mice, the localization of the IL-18 receptor complex in neurons and the neuronal expression of decoy isoforms of the receptor subunits are beginning to reveal the complexity and the significance of the IL-18 system in the CNS. This review summarizes current knowledge on the central role of IL-18 in health and disease.

Elevated systemic interleukin-18 in multiple injured patients is not related to clinical outcome

Interleukin-18 (IL-18) is a pleiotropic proinflammatory cytokine with the ability to induce interferon-gamma production in T-helper cells type 1 and natural killer cells. To investigate the role of IL-18 after severe trauma we measured plasma levels of IL-18 in 229 multiple injured patients [mean age of 39 +/- 16 (range 11-81) years, injury severity score (ISS) of 31 +/- 10 (range 16-66) points; 55 women and 174 men] and correlated these with demographics, clinical course, and routine laboratory parameters. IL-18 plasma levels were significantly increased in polytraumatized patients compared to healthy donors (p < 0.001). Survivors presented significantly (p < 0.05) higher IL-18 plasma median values (n = 193, median 98 pg/mL) compared to nonsurvivors (n = 36, median 63 pg/mL). Patients >60 years old (n = 35) had significantly lower plasma levels of IL-18 (median 45 pg/mL) compared to younger ones (n = 194, median 92 pg/mL). In the subgroup of nonsurvivors (n = 12) elderly patients had the lowest plasma levels of IL-18 (median 45 pg/mL). Patients with an ISS >25 had significant higher IL-18 plasma levels compared to the group with an ISS <or=25 (p < 0.001). Our data demonstrate elevated plasma levels of IL-18 after severe trauma.

Sex differences in the genetic architecture of susceptibility to Cryptococcus neoformans pulmonary infection

Cryptococcus neoformans is a major cause of fungal pneumonia, meningitis and disseminated disease in the immune compromised host. Here we have used a clinically relevant model to investigate the genetic determinants of susceptibility to progressive cryptococcal pneumonia in C57BL/6J and CBA/J inbred mice. At 5 weeks after infection, the lung fungal burden was over 1000-fold higher in C57BL/6J compared to CBA/J mice. A genome-wide scan performed on 210 male and 203 female (CBA/J x C57BL/6J) F2 progeny using lung colony-forming units as a quantitative trait revealed a sex difference in genetic architecture with three loci (designated Cnes1-Cnes3) associated with susceptibility to cryptococcal pneumonia. Single locus analysis identified significant loci on chromosomes 3 (Cnes1) and 17 (Cnes2) with logarithm of the odds (LOD) scores of 4.09 (P=0.0110) and 7.30 (P<0.0001) that explained 8.9 and 15.9% of the phenotypic variance, respectively, in female CBAB6F2 and one significant locus on chromosome 17 (Cnes3) with a LOD score of 4.04 (P=0.010) that explained 8.6% of the phenotypic variance in male CBAB6F2 mice. Genome-wide pair-wise analysis revealed significant quantitative trait locus interactions in both the female and male CBAB6F2 progeny that collectively explained 43.8 and 19.5% of phenotypic variance in each sex, respectively.

Enhanced gastric IL-18 mRNA expression in Helicobacter pylori-infected children is associated with macrophage infiltration, IL-8, and IL-1 beta mRNA expression

OBJECTIVE

To investigate IL-18 mRNA expression in the gastric mucosa in Helicobacter pylori-infected children and its association with macrophage infiltration, IL-8, and IL-1 beta mRNA expression.

METHODS

From 39 children, blood samples were taken for IL-1 beta gene polymorphism analysis and antral biopsies were obtained for histology (including macrophage immunostaining), culture and semiquantitative analysis of IL-18, IL-8, IL-1 beta, and CD14 mRNA expression by reverse transcription-PCR (RT-PCR). RT-PCR was used for H. pylori ureA and cagA mRNA detection in gastric tissue.

RESULTS

H. pylori-infected patients had significantly higher IL-18, IL-8, and IL-1 beta transcript levels and macrophage numbers in the antral mucosa than H. pylori-negative children. IL-1 beta-511/31 gene polymorphism had no impact on gastric IL-1 beta mRNA levels. IL-18 mRNA expression correlated with mRNA expression of IL-8 and IL-1 beta, and transcript levels of all three cytokines were associated with macrophage infiltration and CD14 mRNA expression in the gastric tissue. Significant correlation was also observed between macrophage numbers and histological parameters of gastritis.

CONCLUSION

These results suggest that interleukin(IL)-18 and macrophages may have an important function in gastric inflammatory response to H. pylori infection in children. IL-18, and possibly CD14 receptor signalling pathway, may be involved in macrophage activation and subsequent IL-8 and IL-1 beta release.

Interleukin 18 and periodontal disease

Cytokines are of major importance in periodontal disease progression. It is generally agreed that control of the Th1/Th2 balance is central to the immunoregulation of periodontal disease. There is increasing evidence in humans that the stable periodontal lesion is mediated by Th1 cells, while the progressive lesion sees a shift toward Th2 cells. Equally, there is conflicting evidence, mainly in animal models, that bone loss is mediated by Th1 responses, and that Th2 responses are protective. In the presence of IL-12, IL-18 induces Th1 responses while, in the absence of IL-12, it promotes Th2 responses. It is clear, therefore, that since IL-18 has the ability to induce either Th1 or Th2 differentiation, it becomes important to consider its role in periodontal disease. This review endeavors to give an overview of this cytokine and its relevance for periodontal disease.

Cryptosporidium parvum: The contribution of Th1-inducing pathways to the resolution of infection in mice

The contribution of cytokines IL-12, IL-18, IL-23, and IFN-gamma, and Stat1 signaling molecules involved in Th1 responses associated with host resistance to Cryptosporidium parvum infection was investigated in adult IL-12p40(-/-)mice. Host resistance to C. parvum infection was assessed in different mouse strains lacking IL-12, IL-18, and IL-23 genes. We found that as in IL-12p40(-/-) mice (which lack both IL-12 and IL-23), IL-12p35(-/-) mice (which lack IL-12) and IL-18 deficient mice were also susceptible to infection with C. parvum. Varied levels of resistance were observed when mice were treated with cytokines like IL-18, IL-23 and IFN-gamma. Mice treated with IL-12, as expected, were completely resistant to infection until day 5 post infection, and had significantly decreased (85%) parasite loads at peak infection (day 7), whereas rIL-23 had a lesser effect, decreasing parasite load by approximately 45%. Interestingly, IL-18 appears to play a significant role in initial immune response, even in the absence of IL-12, since treatment with IL-18 in IL-12p40(-/-) knockout mice decreased parasite load by approximately 70%. In addition, the establishment of C. parvum infection in mice lacking the Stat1 gene demonstrated the involvement of this pathway in resolution of infection. These observations indicate a strong requirement for Th1 response in the development of immunity to C. parvum in the adult IL-12p40(-/-) mice, information that will be essential to further investigate the immune responses during infections and in the development of potential vaccine candidates.

A transcriptomic and proteomic analysis of the effect of CpG-ODN on human THP-1 monocytic leukemia cells

The CpG motif of bacterial DNA (CpG-DNA) is a potent immunostimulating agent whose mechanism of action is not yet clear. Here, we used both DNA microarray and proteomic approaches to investigate the effects of oligodeoxynucleotides containing the CpG motif (CpG-ODN) on gene transcription and protein expression profiles of CpG-ODN responsive THP-1 cells. Microarray analysis revealed that 2 h stimulation with CpG-ODN up-regulated 50 genes and down-regulated five genes. These genes were identified as being associated with inflammation, antimicrobial defense, transcriptional regulation, signal transduction, tumor progression, cell differentiation, proteolysis and metabolism. Longer stimulation (8 h) with CpG-ODN enhanced transcriptional expression of 58 genes. Among these 58 genes, none except one, namely WNTI inducible signaling pathway protein 2, was the same as those induced after 2 h stimulation. Proteomic analysis by two-dimensional gel electrophoresis, followed by mass spectrometry identified several proteins up-regulated by CpG-ODN. These proteins included heat shock proteins, modulators of inflammation, metabolic proteins and energy pathway proteins. Comparison of microarray and proteomic expression profiles showed poor correlation. Use of more reliable and sensitive analyses, such as reverse transcriptase polymerase chain reaction, Western blotting and functional assays, on several genes and proteins, nonetheless, confirmed that there is indeed good correlation between mRNA and protein expression after CpG-ODN treatment. This study also revealed that several anti-apoptotic and neuroprotective related proteins, not previously reported, are activated by CpG-DNA. These findings have extended our knowledge on the activation of cells by CpG-DNA and may contribute to further understanding of mechanisms that link innate immunity with acquired immune response(s).

Identifying modulators of hERG channel activity using the PatchXpress planar patch clamp

The authors used the PatchXpress 7000A system to measure compound activity at the hERG channel using procedures that mimicked the "gold-standard" conventional whole-cell patch clamp. A set of 70 compounds, including hERG antagonists with potencies spanning 3 orders of magnitude, were tested on hERG302-HEK cells using protocols aimed at either identifying compound activity at a single concentration or obtaining compound potency from a cumulative concentration dependence paradigm. After exposure to compounds and subsequent washout of the wells to determine reversibility of the block, blockade by a reference compound served as a quality control. Electrical parameters and voltage dependence were similar to those obtained using a conventional whole-cell patch clamp. Rank order of compound potency was also comparable to that determined by conventional methods. One exception was flunarizine, a particularly lipophilic compound. The PatchXpress accurately identified the activity of 29 moderately potent antagonists, which only weakly displace radiolabeled astemizole and are false negatives in the binding assay. Finally, no false hits were observed from a collection of relatively inactive compounds. High-quality data acquisition by PatchXpress should help accelerate secondary screening for ion channel modulators and the drug discovery process.

Rabies virus stimulates nitric oxide production and CXC chemokine ligand 10 expression in macrophages through activation of extracellular signal-regulated kinases 1 and 2

Macrophages represent an essential part of innate immunity, and the viral infection of macrophages results in the release of multiple proinflammatory mediators, such as nitric oxide (NO), cytokines, and chemokines. This study was undertaken to define the molecular mechanism of macrophage activation in response to rabies virus (RV) infection. In RAW264 murine macrophage cells, a well-characterized macrophage model, RV replication was strictly restricted, whereas cell proliferation was significantly enhanced upon RV inoculation. Transcriptional analyses for the expression of inducible forms of NO synthase (iNOS), cytokines, and chemokines revealed that RV virions potentiate the gene expression of iNOS and CXC chemokine ligand 10 (CXCL10), a major chemoattractant of T helper cell type 1. However, RV stimulation had little or no effect on the expression profiles of proinflammatory cytokines and other types of chemokines. In macrophages stimulated with UV-inactivated RV virions, as well as infectious viruses, the phosphorylation of extracellular signal-regulated kinase (ERK) 1 and 2, members of the mitogen-activated protein kinase family, was significantly induced. Specific inhibitors of MAPK/ERK kinase reduced the RV-induced production of NO and CXCL10. Furthermore, the RV-induced activation of the ERK1/2 pathway was severely impaired by the neutralization of the endosomal and lysosomal pH environment with lysosomotropic agents, indicating that endocytosis is a key step leading to the activation of ERK1/2 signaling. Taken together, these results suggest that the ERK1/2-mediated signaling pathway plays a cardinal role in the selective activation of macrophages in response to RV virions, thereby regulating cellular functions during virus infection.

Interferon-γ production and host protective response against Mycobacterium tuberculosis in mice lacking both IL-12p40 and IL-18

Interferon (IFN)-gamma plays an essential role in host defense against infection with Mycobacterium tuberculosis, and its synthesis is critically regulated by interleukin (IL)-12, IL-18 and the recently identified IL-23. The present study was designed to determine the roles of these cytokines in IFN-gamma-mediated host defenses against M. tuberculosis. For this purpose, we compared host protective responses in IL-12p40 and IL-18 double-knockout (DKO) mice (which lacked both IL-12/IL-18 and also IL-23) and IFN-gamma gene-disrupted (GKO) mice. DKO mice were more resistant to the infection than GKO mice, as indicated by their extended survival and reduced live colony numbers in spleen, liver and lung. IFN-gamma was detected by ELISA in liver and lung homogenates, but not in spleen and serum, and in all organs by RT-PCR in DKO mice at comparable or reduced levels to those in wild-type mice. IFN-gamma production was reduced by depletion of CD4+ T cells, but not of natural killer (NK), NKT, gammadeltaT and dendritic cells. Neutralization of IFN-gamma or TNF-alpha by specific monoclonal antibodies (mAbs) significantly shortened the survival time of the infected DKO mice. Furthermore, anti-TNF-alpha mAb partially attenuated IFN-gamma synthesis in the liver of these mice. Finally, the expression level of inducible nitric oxide synthase (iNOS) mRNA in the spleen, liver and lung was considerable in DKO mice but only marginal or undetected in GKO mice. Our results indicate the presence of IL-12-, IL-18- and IL-23-independent host protective responses against mycobacterial infection mediated by IFN-gamma, which was secreted from helper T cells.

Promising immunotherapies with Th1-related cytokines against infectious diseases

In recent years, there has been an increase in the number of individuals with compromised immune systems. This is due to the rise in the numbers of aging people, patients receiving immunosuppressive treatment after organ transplantation, patients with hematological malignancies, and patients with AIDS. These individuals frequently fall into helper T cell (Th)1-Th2 cytokine imbalance due to a shift towards a Th2-dominant condition. Such a pathological condition puts them at a high risk for developing infectious diseases caused by a variety of microbial pathogens which are often refractory to conventional chemotherapy. Therefore, the administration of Th1-related cytokines is expected to be promising immunotherapy against these intractable infectious diseases. In a series of investigations, we have demonstrated the effectiveness of treatment with Th1-related cytokines, such as interferon (IFN)-gamma, interleukin (IL)-12, and IL-18, in protecting animals from experimental infectious diseases caused by Mycobacterium tuberculosis and Cryptococcus neoformans. Recently, several investigators reported successful clinical treatment with IFN-gamma or IL-12 in patients with intractable tuberculous and nontuberculous mycobacteriosis. Thus, now is an appropriate time for scientific evaluation to clinically confirm the effectiveness of these novel immunotherapies.