Meeting Report

Immunology and Cell Biology (2012) 90, 751–754; doi:10.1038/icb.2012.40; published online 31 July 2012

Advances in infection and immunity: from bench to bedside

Diana S Hansen1, Cameron R Stewart2, Anthony Jaworowski3 and Tania F de-Koning Ward4

  1. 1Infection and Immunity Division, The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
  2. 2CSIRO Australian Animal Health Laboratory, East Geelong, Victoria, Australia
  3. 3Centre for Virology, Burnet Institute, Melbourne, Victoria, Australia
  4. 4Molecular and Medical Research Strategic Research Centre, Deakin University, Waurn Ponds, Victoria, Australia

Correspondence: Dr DS Hansen, The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia. E-mail: hansen@wehi.edu.au

Received 9 May 2012; Revised 5 July 2012; Accepted 6 July 2012
Advance online publication 31 July 2012

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Abstract

This report summarizes recent advances on host–pathogen interactions, innate and adaptive responses to infection, as well as novel strategies for the control of infectious diseases.

Keywords:

pathogen; infection; immunity

Following the successful inaugural Lorne Infection and Immunity Conference in 2011, scientists have gathered again on 15–17 February 2012 for a second round of this multidisciplinary international meeting. Sessions covered a range of different topics, including innate and adaptive immune responses to infection, host–pathogen interactions, systems biology, as well as clinical and translational research. Here we summarize some of the main concepts discussed at the meeting and the progress on the development of new therapeutic approaches for the control of infectious diseases.

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Microbial pathogenesis

Microbial pathogens have developed many elaborate mechanisms to establish infection. Work presented by V Sperandio (Dallas, TX, USA) revealed how complex these processes can be, with enterohaemorrhagic Escherichia coli (EHEC) relying on two inter-kingdom chemical signalling systems from its host and microbial flora to modulate expression of its own virulence and metabolic genes. EHEC causes food-borne diseases, which may lead to life-threatening illnesses such as haemolytic uraemic syndrome. During the growth of EHEC within the intestine, host-derived fucose, which is made available to microbiota such as Bacteroides thetaiotaomicro, is supplied in turn to EHEC to modulate the expression of the locus of enterocyte effacement (LEE) genes. The expression of virulence genes from this locus leads to the formation of the characteristic attaching and effacing lesions by EHEC on epithelial cells.

Another strain of E. coli termed uropathogenic E. coli is the leading cause of urinary tract infections in humans. M Totsika (Brisbane, Queensland, Australia) reported that the genome of the virulent E. coli ST131 strain contains most of the hallmark virulence genes of uropathogenic E. coli, allowing this pathogen to survive inside bladder cells for prolonged periods of time. As colonization of the bladder by E. coli ST131 requires expression of type 1 fimbriae, this provides a promising candidate for strategies aimed at preventing its adherence and subsequent ability to establish cystitis.

Other examples of virulence factors were also identified in more complex organisms, such as Plasmodium, the causative agent of malaria. In the context of his recently published reverse genetics analysis of the kinome of P. falciparum,1 C Doerig (Melbourne, Victoria, Australia) generated parasite lines expressing individual kinases fused to various tags to investigate the localization of these enzymes. P. falciparum PfTKL2, a kinase of the tyrosine kinase-like kinase group, which in phylogenetic analysis strongly clusters with mammalian interleukin-receptor-associated kinases, was found to be secreted by infected erythrocytes. Interleukin-receptor-associated kinases are the key mediators of Toll-like receptor (TLR) signalling, suggesting the intriguing possibility that PfTKL2 might have a role in modulating TLR signalling in bystander immune or endothelial cells.

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Imaging host–pathogen interactions

The resolution of viral infections and protection from re-infection is dependent upon adequate T-cell responses. For peripheral tissues such as the skin, both migrating and memory T cells have been implicated in long-term immunity. This was illustrated by S Mueller (Melbourne, Victoria, Australia) who infected the skin of mice with herpes simplex virus type 1 and analysed T-cell responses by two-photon microscopy. Two distinct virus-specific memory subsets were identified by this approach: a slow-moving population of CD8+ T cells that were resident in the epidermis and confined largely to the site of infection, and a dynamic population of CD4+ T cells that trafficked rapidly through the dermis as part of a wider recirculation pattern. The expression of unique homing-molecules by recirculating CD4+ T-effector memory cells mirrored their migratory capacity and their ability to enter skin sites long after viral clearance, mediating protection from re-infection.

Central to the replication of viruses is the trafficking of proteins in and out of the nucleus through the importin superfamily of transporters. Although replication of RNA viruses generally occurs in the cytoplasm, Wagstaff, Jans and colleagues (Melbourne, Victoria, Australia) have shown using in vivo imaging approaches that RNA viruses such as HIV-1 and Dengue express gene products that traffic into the host cell nucleus through the action of specific targeting sequences and importins. This has enabled their laboratory to generate specific inhibitors of viral protein nuclear trafficking,2 which in turn will provide strategies to combat viral infection.

Other sophisticated forms of imaging were also presented at the conference, including single-molecule signalling in intact cells to gain insight into the molecular mechanisms of T-cell function. Activation of T cells begins with the formation of signalling complexes at the cell surface, involving the T-cell receptor, the Src family kinase Lck and the adaptor protein (linker for activation of T cells). By using super-resolution fluorescence microscopy,3 K Gaus (Sydney, New South Wales, Australia) has been able to localize individual proteins followed by quantitative cluster analysis to establish how T-cell signalling complexes are assembled upon receptor triggering.

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Innate pathogen recognition

There has been great progress in our understanding of molecules mediating innate immune responses in the past 10 years. During an entertaining plenary session L O’Neill (Dublin, Ireland) gave three examples of how insights into TLRs and the related inflammasome complexes are helping us in our understanding of infectious diseases. The first example involved a description of how the TLR2/TLR4 adaptor Mal is required to maintain the epithelial barrier in the gut. Deletion of Mal in mice or inhibition in vitro allow Salmonella to disseminate across the epithelium. This is a new function for Mal, as it involves the regulation of tight junction proteins. The second example described how in type 2 diabetes, an amyloid protein (IAPP) is sensed by the Nlrp3 inflammasome driving interleukin (IL)-1β production. IL-1β is implicated in the insulin resistance and β-cell loss in type 2 diabetes, and this finding provides a mechanism for the induction of this cytokine. Finally, Professor O’Neill described how lipopolysaccharide-dependent TLR4-signalling alters macrophage metabolism, promoting a high rate of glycolysis (Warburg effect). This leads to an accumulation of succinate, which in turn activates the transcription factor hypoxia-inducible factor-1α. A key target gene is pro-IL-1β. Thus, this work reveals a metabolic process required for inflammation, which, in effect, is acting as a danger signal from mitochondria. These exciting findings reveal new processes that might be amenable to therapeutic targeting.

Other aspects of TLR-pathogen interactions were presented by M Sweet (Brisbane, Queensland, Australia), who studied differential innate immune responses to lipopolysaccharide in human and mouse macrophages, exploring the concept that species-specific responses represent, in part, the co-evolution of host and pathogen.4 These genome-wide transcriptome studies revealed genuine differences in human and mouse TLR responses, and implicate previously unappreciated pathways, such as copper homoeostasis, in innate immune responses. The recognition of pathogenic Mycobacteria by TLRs was illustrated by A Blumenthal (Brisbane, Queensland, Australia). Her group has shown that RP105, a molecule that shares structural features with the TLR family of receptors, aids TLR2-mediated macrophage responses to Mycobacterium tuberculosis and Mycobacterium bovis. Their data suggest that RP105 physically interacts with TLR2 and that both receptors are required for optimum secretion of tumour necrosis factor.

The pivotal innate immune process of natural killer (NK) cell recognition of virally infected cells is achieved by the interaction of peptide-laden human leukocyte antigen class I molecules with members of the killer immunoglobulin receptor (KIR) family. A particular domain within the peptide-laden human leukocyte antigen, the three-domain KIR family (KIR3D) is critical for this process as demonstrated by the link between allelic variation of KIR3D and control of HIV-1 replication. A Brooks (Melbourne, Victoria, Australia) described the structure of the KIR3DL1 receptor bound to HLA-B*5701 associated with a self-peptide. This recent study5 provides a framework for understanding the interplay between peptide variability as well as KIR and HLA polymorphism in determining the specificity requirements of this interaction.

C Biron (Providence, RI, USA) presented work characterizing how immunological experience conditions NK cell responses to viral infections. Her group demonstrated that under conditions of extended viral infections, the presence of an activating receptor on the NK cell and a ligand on a virus-infected target cell helps select NK cell subsets for expansion and maintenance. These findings provide evidence that innate immune responses to infection can be regulated not only by polymorphic NK cell receptors but also by previous immunological experience.

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Adaptive immune responses in the control infection and immunopathology

Certain pathogens are difficult to eradicate and require a strong immune response, which might result in adverse effects and immunopathology. For example, blood-stage malaria infections are characterized by excessive inflammation that contributes to the induction of severe malaria. The anti-inflammatory cytokine IL-10 has an important role in the control of inflammation in the Plasmodium chabaudi chabaudi AS mouse infection model. Recent work presented by J Langhorne (London, UK) identified interferon-γ+CD4+ Th1 cells as the essential and sufficient source of IL-10 during infection able to prevent severe immune-mediated pathology.6

During the response to viral infections, cytotoxic CD8+ T cells undergo a programme of differentiation that results in regulated expression of multiple effector genes. The molecular processes underlying the acquisition of cytotoxic CD8+ T cells effector gene expression are not clearly defined. Recent findings by S Turner (Melbourne, Victoria, Australia) revealed that whereas naive cytotoxic CD8+ T cells precursors predominantly produce tumour necrosis factor-α, their production of interferon-γ responses depends on continued lymphocyte proliferation. This proliferation-dependent switch of cytokine production patterns appears to be under the control of epigenetic changes within the ifnG and tnfA promoter regions.7

Novel aspects on CD8+ T-cell development were uncovered by R Gugasyan (Melbourne, Victoria, Australia) who reported that mice lacking nuclear factor-κB1 develop a unique population of CD8+ T cells that display innate T-cell properties and populate peripheral immune organs.8 Development of this innate-like population coincides with changes in CD8+ T-cell selection, including a dependence on major histocompatibility complex class Ia or Ib molecules expressed by hematopoietic cells.

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Clinical and translational research

Several presentations described ongoing work in clinical settings aimed at developing new tools to control various diseases, including pneumococcal and hepatitis C virus (HCV) infections. It is estimated that over 240000 Australians are infected with HCV. The HCV Networks study being conducted by M Hellard (Melbourne, Victoria, Australia) is investigating HCV transmission dynamics in a cohort of people who inject drugs, and measuring the factors that impact on HCV clearance and re-infection. Key findings to date include that HCV re-infection is far more common than previously recognized, that clearance does not always occur following HCV re-infection, and that the structure of the PWID network impacts on the rate of HCV transmission within the group. The results of the HCV Networks study are informing public health interventions, vaccine development and the roll out of HCV treatment.

Existing pneumococcal vaccines targeting the serologically variable capsular polysaccharide have serious shortcomings, including restricted serotype coverage and high production costs. Vaccines based on conserved pneumococcal protein antigens may be cheaper and more effective. Dozens of candidate antigens have been identified using reverse vaccinology approaches and genome-wide in vivo screens. J Paton (Adelaide, South Australia, Australia) presented data aimed at fast-tracking development of a vaccine comprising derivatives of the pneumococcal toxin pneumolysin and major surface proteins PspA and CbpA. Preclinical data demonstrated protective activity across serotypes and increased efficacy when used in combination with each other. The strongest protection was elicited by a fusion protein comprising detoxified pneumolysin, flanked by CbpA epitopes, and a conserved region of PspA.

Multidrug-resistant pathogens are a major health issue and effective broad-spectrum drugs are urgently needed. M Cooper (Brisbane, Queensland, Australia) reported a novel lipidomic strategy for discovery of anti-bacterial drugs. The approach involves the production of a library of membrane-derived lipid extracts, which enables the identification of peptide sequences with selective binding for bacterial membranes using phage display screening. Novel anti-bacterial drugs have emerged after linking selected peptides to antibiotics. The new compounds have activities 100- to 1000-fold greater than the original antibiotic, with promising toxicology and plasma stability.

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Emerging infectious diseases

The mosquito-borne West Nile Virus causes outbreaks of fever and encephalitis in humans and horses. An attenuated strain of West Nile Virus, Kunjin (KUNV) is endemic in Northern Australia and infection with this virus is generally associated with mild symptoms. However, in February 2011, a virulent strain of West Nile Virus (NSW2011) appeared in horses in New South Wales, displaying typical symptoms of encephalitis and causing death in 10–15% of cases. A Khromykh (Brisbane, Queensland, Australia) described the increased virulence and pathogenicity of NSW2011 compared with KUNV in mice, and is currently investigating the origins of pathogenic determinants within NSW2011.

Hendra virus is a highly pathogenic paramyxovirus also infecting horses and humans. In 2011, 18 separate outbreaks of Hendra virus occurred in horses in Queensland and New South Wales, Australia. The pathogenic nature of Hendra virus in humans, the transmission of this virus to humans from horses and the paucity of treatments highlights the importance of understanding this infection more clearly. C Stewart (Geelong, Victoria, Australia) described the current understanding of the host microRNA responses to Hendra virus infection in human cells, and their potential roles in modulating immune responses, virus replication and prospective roles in diagnosis.

The theme of host responses to recently emergent pathogens continued with mention of an epidemic, ‘hypervirulent’ strain of Clostridium difficile. Using the BI/NAP1/027 epidemic isolate and mouse infection models, A Chakravorty (Melbourne, Victoria, Australia) described that both innate and adaptive immune responses are elicited during C. difficile infection. The specific effects that individual bacterial toxins have on modulating immune responses is currently being investigated.

Dengue is a major cause of paediatric hospitalizations in Vietnam. C Simmons (Oxford, UK) reported on findings from epidemiological studies of dengue infection in this setting and on human-to-mosquito transmission of the virus. The main findings revealed the importance of young age, female gender and genetic variation at the major histocompatibility complex class I polypeptide-related sequence B and phospholipase-c epsilon-1 in the epidemiological risk of developing severe dengue. Transmission studies revealed an inverse relationship between viremia in the human host and the mosquito extrinsic incubation period, suggesting the possibility that individuals with high viral loads could act as ‘superspreaders’ of infection by accelerating the capacity of vectors to transmit the virus.

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Systems biology: new approaches for development of therapies to control infection

The role of individual variation in immune responses as a determinant of infectious disease outcome has long been appreciated, but it is only recently that such information has become of great interest in clinical settings. D Nolan (Perth, Western Australia, Australia) discussed a recent example in which genome-wide associated studies revealed that polymorphisms in the IL-28B locus have a dramatic impact on HCV infection outcomes. New insights into the mechanism by which IL-28 modules susceptibility of hepatitis C revealed that this cytokine appears to modulate interferon responses required for the efficient control of infection.

Another interesting example was provided by T Lawley (Welcome Trust Sanger Institute, UK), who conducted a comprehensive microbiota analysis of mice infected with a hypervirulent strain of C. difficile (027/BI), which induces chronic dysbiosis. The main findings revealed that infection with the 027/BI strain is associated with the emergence of a distinct intestinal microbiota. Treatment of dysbiosis-affected mice with faeces from healthy donors restored microbiota diversity and resolved pathology. Studies are now underway to design a mixture of bacteria amenable to in vitro culture that can re-establish a healthy microbiota and eradicate persistent C. difficile infection from susceptible mice.

APOBEC3G is a cellular factor that restricts permissiveness to HIV infection. The HIV accessory protein Vif prevents incorporation of APOBEC3G into assembling virions and thereby allows viral replication. Vif recruits an E3 ubiquitin ligase complex and targets APOBEC3G for proteosomal degradation. Recent studies presented by R Harris (Minneapolis, MN, USA) allowed identification of the cellular transcription factor core-binding factor-β as an integral part of the Vif-E3-ubiquitin ligation complex. These findings create new opportunities for drug development for the control of retroviruses.

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Concluding remarks

Infectious diseases remain a significant cause of global health, economic and social problems. Many of the findings discussed at the Lorne Infection and Immunity 2012 Meeting illustrate how multidisciplinary approaches are not only addressing fundamental questions associated with pathogenesis and immunity to infection, but also facilitating the translation of those findings into clinical studies for the prevention and treatment of disease.

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References

  1. Solyakov L, Halbert J, Alam MM, Semblat JP, Dorin-Semblat D, Reininger L et al. Global kinomic and phospho-proteomic analyses of the human malaria parasite Plasmodium falciparum. Nat Commun 2011; 2: 565. | Article | PubMed |
  2. Wagstaff KM, Rawlinson SM, Hearps AC, Jans DA. An AlphaScreen(R)-based assay for high-throughput screening for specific inhibitors of nuclear import. J Biomol Screen 2011; 16: 192–200. | Article | PubMed |
  3. Williamson DJ, Owen DM, Rossy J, Magenau A, Wehrmann M, Gooding JJ et al. Pre-existing clusters of the adaptor Lat do not participate in early T cell signaling events. Nat Immunol 2011; 12: 655–662. | Article | PubMed | CAS |
  4. Schroder K, Irvine KM, Taylor MS, Bokil NJ, Le Cao KA, Masterman KA et al. Conservation and divergence in Toll-like receptor 4-regulated gene expression in primary human versus mouse macrophages. Proc Natl Acad Sci USA 2012; 109: E944–E953. | Article | PubMed |
  5. Vivian JP, Duncan RC, Berry R, O’Connor GM, Reid HH, Beddoe T et al. Killer cell immunoglobulin-like receptor 3DL1-mediated recognition of human leukocyte antigen B. Nature 2011; 479: 401–405. | Article | PubMed |
  6. Freitas do Rosario AP, Lamb T, Spence P, Stephens R, Lang A, Roers A et al. IL-27 promotes IL-10 production by effector Th1 CD4+ T cells: a critical mechanism for protection from severe immunopathology during malaria infection. J Immunol 2012; 188: 1178–1190. | Article | PubMed |
  7. Denton AE, Russ BE, Doherty PC, Rao S, Turner SJ. Differentiation-dependent functional and epigenetic landscapes for cytokine genes in virus-specific CD8+ T cells. Proc Natl Acad Sci USA 2011; 108: 15306–15311. | Article | PubMed |
  8. Gugasyan R, Horat E, Kinkel SA, Ross F, Grigoriadis G, Gray D et al. The NF-kappaB1 transcription factor prevents the intrathymic development of CD8 T cells with memory properties. EMBO J 2012; 31: 692–706. | Article |
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Acknowledgements

We apologize to those presenters whose work could not be included in the report due to space constraints. The 2012 Lorne Infection and Immunity Conference was hosted by the Victorian Infection and Immunity Network and sponsored by CSL and Gilead Life Research.