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Witte CE, Archer KA, Rae CS, Sauer JD, Woodward JJ, Portnoy DA. Innate immune pathways triggered by Listeria monocytogenes and their role in the induction of cell-mediated immunity. Adv Immunol 2012; 113:135-56. [PMID: 22244582 DOI: 10.1016/b978-0-12-394590-7.00002-6] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Acquired cell-mediated immunity to Listeria monocytogenes is induced by infection with live, replicating bacteria that grow in the host cell cytosol, whereas killed bacteria, or those trapped in a phagosome, fail to induce protective immunity. In this chapter, we focus on how L. monocytogenes is sensed by the innate immune system, with the presumption that innate immunity affects the development of acquired immunity. Infection by L. monocytogenes induces three innate immune pathways: an MyD88-dependent pathway emanating from a phagosome leading to expression of inflammatory cytokines; a STING/IRF3-dependent pathway emanating from the cytosol leading to the expression of IFN-β and coregulated genes; and very low levels of a Caspase-1-dependent, AIM2-dependent inflammasome pathway resulting in proteolytic activation and secretion of IL-1β and IL-18 and pyroptotic cell death. Using a combination of genetics and biochemistry, we identified the listerial ligand that activates the STING/IRF3 pathway as secreted cyclic diadenosine monophosphate, a newly discovered conserved bacterial signaling molecule. We also identified L. monocytogenes mutants that caused robust inflammasome activation due to bacteriolysis in the cytosol, release of DNA, and activation of the AIM2 inflammasome. A strain was constructed that ectopically expressed and secreted a fusion protein containing Legionella pneumophila flagellin that robustly activated the Nlrc4-dependent inflammasome and was highly attenuated in mice, also in an Nlrc4-dependent manner. Surprisingly, this strain was a poor inducer of adaptive immunity, suggesting that inflammasome activation is not necessary to induce cell-mediated immunity and may even be detrimental under some conditions. To the best of our knowledge, no single innate immune pathway is necessary to mount a robust acquired immune response to L. monocytogenes infection.
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Affiliation(s)
- Chelsea E Witte
- Graduate Group in Microbiology, University of California, Berkeley, Berkeley, California, USA
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52
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Li J, Hu M, Guo J, Su Z, Wei Q. Calcineurin subunit B is an immunostimulatory protein and acts as a vaccine adjuvant inducing protective cellular and humoral responses against pneumococcal infection. Immunol Lett 2011; 140:52-8. [DOI: 10.1016/j.imlet.2011.06.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2011] [Revised: 05/23/2011] [Accepted: 06/10/2011] [Indexed: 12/01/2022]
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Abstract
The implementation of vaccination as an empiric strategy to protect against infectious diseases was introduced even before the advent of hygiene and antimicrobials in the medical practice. Nevertheless, it was not until a few decades ago that we really started understanding the underlying mechanisms of protection triggered by vaccination. Vaccines were initially based on attenuated or inactivated organisms. Subunit vaccines were then introduced as more refined formulations, exhibiting improved safety profiles. However, purified antigens tend to be poorly immunogenic and often require the use of adjuvants to achieve adequate stimulation of the immune system. Vaccination strategies, such as mucosal administration, also require potent adjuvants to improve performance. In the 1990s, immunologists found that pathogens could be sensed as ‘danger signals’ by receptors recognizing conserved motifs. Although our knowledge is still limited, tremendous advances were made in the understanding of host defence mechanisms regulated by these evolutionary conserved receptors, and the molecular structures which are recognized by them. This opened a new era in adjuvant development. Some of the latest players arrived to this field are the cyclic di‐nucleotides, which are ubiquitous prokaryotic intracellular signalling molecules. This review is focused on their potential for the development of vaccines and immunotherapies.
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Affiliation(s)
- Rimma Libanova
- Department of Vaccinology and Applied Microbiology, Helmholtz Centre for Infection Research, 38124 Braunschweig, Germany.
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Jin L, Hill KK, Filak H, Mogan J, Knowles H, Zhang B, Perraud AL, Cambier JC, Lenz LL. MPYS is required for IFN response factor 3 activation and type I IFN production in the response of cultured phagocytes to bacterial second messengers cyclic-di-AMP and cyclic-di-GMP. THE JOURNAL OF IMMUNOLOGY 2011; 187:2595-601. [PMID: 21813776 DOI: 10.4049/jimmunol.1100088] [Citation(s) in RCA: 226] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Cyclic-di-GMP and cyclic-di-AMP are second messengers produced by bacteria and influence bacterial cell survival, differentiation, colonization, biofilm formation, virulence, and bacteria-host interactions. In this study, we show that in both RAW264.7 macrophage cells and primary bone marrow-derived macrophages, the production of IFN-β and IL-6, but not TNF, in response to cyclic-di-AMP and cyclic-di-GMP requires MPYS (also known as STING, MITA, and TMEM173). Furthermore, expression of MPYS was required for IFN response factor 3 but not NF-κB activation in response to these bacterial metabolites. We also confirm that MPYS is required for type I IFN production by cultured macrophages infected with the intracellular pathogens Listeria monocytogenes and Francisella tularensis. However, during systemic infection with either pathogen, MPYS deficiency did not impact bacterial burdens in infected spleens. Serum IFN-β and IL-6 concentrations in the infected control and MPYS(-/-) mice were also similar at 24 h postinfection, suggesting that these pathogens stimulate MPYS-independent cytokine production during in vivo infection. Our findings indicate that bifurcating MPYS-dependent and -independent pathways mediate sensing of cytosolic bacterial infections.
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Affiliation(s)
- Lei Jin
- Integrated Department of Immunology, University of Colorado Denver School of Medicine, Denver, CO 80206, USA
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55
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Spehr V, Warrass R, Höcherl K, Ilg T. Large-scale production of the immunomodulator c-di-GMP from GMP and ATP by an enzymatic cascade. Appl Biochem Biotechnol 2011; 165:761-75. [PMID: 21710212 DOI: 10.1007/s12010-011-9294-z] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2011] [Accepted: 05/24/2011] [Indexed: 01/04/2023]
Abstract
(3'-5')-Cyclic diguanylate (c-di-GMP) is a bacterial second messenger with immunomodulatory activities in mice suggesting potential applications as a vaccine adjuvant and as a therapeutic agent. Clinical studies in larger animals or humans will require larger doses that are difficult and expensive to generate by currently available chemical or enzymatic synthesis and purification methods. Here we report the production of c-di-GMP at the multi-gram scale from the economical precursors guanosine monophosphate (GMP) and adenosine triphosphate by a "one-pot" three enzyme cascade consisting of GMP kinase, nucleoside diphosphate kinase, and a mutated form of diguanylate cyclase engineered to lack product inhibition. The c-di-GMP was purified to apparent homogeneity by a combination of anion exchange chromatography and solvent precipitation and was characterized by reversed phase high performance liquid chormatography and mass spectrometry, nuclear magnetic resonance spectroscopy, and further compositional analyses. The immunomodulatory activity of the c-di-GMP preparation was confirmed by its potentiating effect on the lipopolysaccharide-induced interleukin 1β, tumor necrosis factor α, and interleukin 6 messenger RNA expression in J774A.1 mouse macrophages.
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Affiliation(s)
- Volker Spehr
- Intervet Innovation GmbH, Zur Propstei, 55270 Schwabenheim, Germany
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56
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Ebensen T, Libanova R, Schulze K, Yevsa T, Morr M, Guzmán CA. Bis-(3',5')-cyclic dimeric adenosine monophosphate: strong Th1/Th2/Th17 promoting mucosal adjuvant. Vaccine 2011; 29:5210-20. [PMID: 21619907 DOI: 10.1016/j.vaccine.2011.05.026] [Citation(s) in RCA: 99] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2010] [Revised: 04/07/2011] [Accepted: 05/11/2011] [Indexed: 12/24/2022]
Abstract
New effective adjuvants are required to improve the performance of subunit vaccines. Here, we showed that bis-(3',5')-cyclic dimeric adenosine monophosphate (c-di-AMP), a second messenger molecule in bacteria and archaea, exerts strong adjuvant activities when delivered by mucosal route. In vitro studies showed that c-di-AMP was able to both stimulate pre-activated murine macrophages and promote the activation and maturation of dendritic cells of murine and human origin. Co-administration of c-di-AMP with β-galactosidase (β-Gal) by intranasal route to BALB/c mice resulted in the elicitation of significantly higher serum antigen-specific IgG titres than in controls. The induction of local immune responses was shown by the production of antigen-specific secretory IgA in different mucosal territories. In addition, strong cellular immune responses were observed against both the β-Gal protein and a peptide encompassing its MHC class I-restricted epitope. The ratio of β-Gal-specific antibodies and the secreted cytokine profiles by in vitro re-stimulated splenocytes suggested that a balanced Th1/Th2/Th17 response pattern is promoted by c-di-AMP. When C57BL/6 mice were immunized with OVA and c-di-AMP, vigorous in vivo CTL responses were also observed. These results indicated that c-di-AMP exhibits a high potential as adjuvant for the development of mucosal vaccines, in particular when cellular immunity is needed.
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Affiliation(s)
- Thomas Ebensen
- Department of Vaccinology and Applied Microbiology, Helmholtz Centre for Infection Research, Braunschweig, Germany.
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57
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Zhao L, KuoLee R, Harris G, Tram K, Yan H, Chen W. c-di-GMP protects against intranasal Acinetobacter baumannii infection in mice by chemokine induction and enhanced neutrophil recruitment. Int Immunopharmacol 2011; 11:1378-83. [PMID: 21496497 DOI: 10.1016/j.intimp.2011.03.024] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2010] [Revised: 03/28/2011] [Accepted: 03/31/2011] [Indexed: 12/25/2022]
Abstract
Acinetobacter baumannii has emerged as a major cause of both community-associated and nosocomial infections worldwide. A. baumannii rapidly develops resistance to multiple antibiotics; as a result, infections by this pathogen have become increasingly difficult to treat. In this study, we evaluated the effect of 3',5'-cyclic diguanylic acid (c-di-GMP), a bacterial second messenger and immunomodulator, in the host defense against A. baumannii infection in a mouse model of intranasal infection. Our results showed that 50 μg of c-di-GMP administered 18 h prior to infection provided the best protection against intranasal infection with A. baumannii. Mechanistically, administration of c-di-GMP induced the production of chemokines KC, MCP-1, MIP-1α, MIP-2 and RANTES, and enhanced neutrophil recruitment in the lung. Moreover, depletion of neutrophils abolished the protective role of c-di-GMP. Taken together, our data suggest that c-di-GMP confers resistance against intranasal A. baumannii infection in mice through a neutrophil-dependent mechanism and that c-di-GMP should be further explored as an immunomodulator for the treatment of A. baumannii infection.
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Affiliation(s)
- Lisa Zhao
- Institute for Biological Sciences, National Research Council Canada, 100 Sussex Drive, Ottawa, Ontario, Canada K1A 0R6
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58
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59
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Ching SM, Tan WJ, Chua KL, Lam Y. Synthesis of cyclic di-nucleotidic acids as potential inhibitors targeting diguanylate cyclase. Bioorg Med Chem 2010; 18:6657-65. [PMID: 20797869 DOI: 10.1016/j.bmc.2010.07.068] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2010] [Revised: 07/28/2010] [Accepted: 07/29/2010] [Indexed: 11/30/2022]
Abstract
Five analogs of cyclic di-nucleotidic acid including c-di-GMP were synthesized and evaluated for their biological activities on Slr1143, a diguanylate cyclase of Synechocystis sp. Slr1143 was overexpressed from the recombinant plasmid which contained the gene of interest and subsequently purified by affinity chromatography. A new HPLC method capable of separating the compound and product peaks with good resolution was optimized and applied to the analysis of the compounds. Results obtained show that cyclic di-inosinylic acid 1b demonstrates a stronger inhibition on Slr1143 than c-di-GMP and is a potential inhibitor for biofilm formation.
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Affiliation(s)
- Shi Min Ching
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
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60
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Zähringer F, Massa C, Schirmer T. Efficient enzymatic production of the bacterial second messenger c-di-GMP by the diguanylate cyclase YdeH from E. coli. Appl Biochem Biotechnol 2010; 163:71-9. [PMID: 20582742 DOI: 10.1007/s12010-010-9017-x] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2010] [Accepted: 06/15/2010] [Indexed: 01/03/2023]
Abstract
Cyclic di-GMP (c-di-GMP) is an almost universal bacterial second messenger involved in the regulation of cell surface-associated traits and the persistence of infections. GGDEF and EAL domain-containing proteins catalyse c-di-GMP synthesis and degradation, respectively. We report the enzymatic large-scale synthesis of c-di-GMP, making use of the GGDEF domain-containing protein YdeH from Escherichia coli. Overexpression and purification of YdeH have been established, and the conditions for c-di-GMP synthesis were optimised. In contrast to the chemical synthesis of c-di-GMP, enzymatic c-di-GMP production is a one-step reaction that can easily be performed with the equipment of a standard biochemical lab. The protocol allows the production of milligram amounts of c-di-GMP within 1 day and paves the way for extensive biochemical and biophysical studies on c-di-GMP-mediated processes.
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Affiliation(s)
- Franziska Zähringer
- Core Program Structural Biology and Biophysics, Biozentrum, University of Basel, Klingelbergstrasse 70, Basel, Switzerland
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61
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Yan H, Chen W. 3',5'-Cyclic diguanylic acid: a small nucleotide that makes big impacts. Chem Soc Rev 2010; 39:2914-24. [PMID: 20577685 DOI: 10.1039/b914942m] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
3',5'-Cyclic diguanylic acid (c-di-GMP) is a naturally occurring small cyclic dinucleotide found in bacteria. There has been a recent surge of interest in the two-component signalling networks involving this molecule. This tutorial review introduces the biosynthesis of c-di-GMP, particularly the conserved domain features involved in its enzymatic synthesis and degradation, cellular functions and phenotypes regulated by c-di-GMP through c-di-GMP-binding proteins. The chemical synthesis and structural studies of c-di-GMP are also summarized. Two potential applications of c-di-GMP, i.e. bacterial biofilm formation and immunostimulation, are surveyed. Recent observations on c-di-GMP-binding riboswitches are also introduced.
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Affiliation(s)
- Hongbin Yan
- Department of Chemistry, Brock University, 500 Glenridge Ave., St. Catharines, Ontario, L2S 3A1, Canada.
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62
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Chen W, Kuolee R, Yan H. The potential of 3',5'-cyclic diguanylic acid (c-di-GMP) as an effective vaccine adjuvant. Vaccine 2010; 28:3080-5. [PMID: 20197136 DOI: 10.1016/j.vaccine.2010.02.081] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2009] [Revised: 02/12/2010] [Accepted: 02/15/2010] [Indexed: 12/27/2022]
Abstract
3', 5'-Cyclic diguanylic acid (c-di-GMP) is a bacterial intracellular signaling molecule that plays a crucial role in the regulation of bacterial motility, adhesion, cell-to-cell communication, exopolysaccharide synthesis, biofilm formation and virulence. The recent finding that c-di-GMP can act as a danger signal on eukaryotic cells has prompted the study of the immunostimulatory and immunomodulatory properties of c-di-GMP in an effort to determine whether c-di-GMP might be further developed as a potential vaccine adjuvant. In this review, we discussed the recent in vitro and in vivo studies of the immunostimulatory properties of c-di-GMP and the progress that has been made in the preclinical development of c-di-GMP as a potential vaccine adjuvant for systemic and mucosal vaccination.
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Affiliation(s)
- Wangxue Chen
- Institute for Biological Sciences, National Research Council Canada, Ottawa, Ontario, Canada.
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63
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Libanova R, Ebensen T, Schulze K, Bruhn D, Nörder M, Yevsa T, Morr M, Guzmán CA. The member of the cyclic di-nucleotide family bis-(3', 5')-cyclic dimeric inosine monophosphate exerts potent activity as mucosal adjuvant. Vaccine 2010; 28:2249-2258. [PMID: 20060510 DOI: 10.1016/j.vaccine.2009.12.045] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2009] [Revised: 12/11/2009] [Accepted: 12/20/2009] [Indexed: 01/01/2023]
Abstract
Here we demonstrated that bis-(3',5')-cyclic dimeric inosine monophosphate (c-di-IMP) exhibits potent adjuvant properties. BALB/c or C57BL/6 mice were immunized with the model antigens beta-galactosidase (beta-Gal) or Ovalbumin (OVA) alone or co-administered with c-di-IMP by the intranasal route. Animals receiving c-di-IMP showed significantly higher anti-beta-Gal or OVA immunoglobulin G titres (IgG) in sera than those vaccinated with beta-Gal or OVA alone. Furthermore, strong local immune responses were also detectable in different mucosal territories, as shown by the high levels of beta-Gal-specific secretory IgA (sIgA). The analysis of the antigen-specific IgG isotypes in sera, together with the profiles of the cytokines and chemokines secreted by lymphocytes from vaccinated animals showed that the use of c-di-IMP resulted in stimulation of a mixed T(H)1/T(H)2/T(H)17 response. Mucosal immunization of C57BL/6 mice with OVA using c-di-IMP as adjuvant also led to the stimulation of strong in vivo CTL responses (i.e., 60% of antigen-specific lysis) [corrected].Our results demonstrated that the novel compound c-di-IMP exhibits strong adjuvant properties when co-administered with an antigen by the mucosal route, thereby representing a promising candidate adjuvant for the development of mucosal vaccination strategies.
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Affiliation(s)
- Rimma Libanova
- Department of Vaccinology and Applied Microbiology, Helmholtz Centre of Infection Research, Inhoffenstrasse 7, D-38124 Braunschweig, Germany
| | - Thomas Ebensen
- Department of Vaccinology and Applied Microbiology, Helmholtz Centre of Infection Research, Inhoffenstrasse 7, D-38124 Braunschweig, Germany.
| | - Kai Schulze
- Department of Vaccinology and Applied Microbiology, Helmholtz Centre of Infection Research, Inhoffenstrasse 7, D-38124 Braunschweig, Germany
| | - Daniela Bruhn
- Department of Vaccinology and Applied Microbiology, Helmholtz Centre of Infection Research, Inhoffenstrasse 7, D-38124 Braunschweig, Germany
| | - Miriam Nörder
- Department of Vaccinology and Applied Microbiology, Helmholtz Centre of Infection Research, Inhoffenstrasse 7, D-38124 Braunschweig, Germany
| | - Tetyana Yevsa
- Department of Vaccinology and Applied Microbiology, Helmholtz Centre of Infection Research, Inhoffenstrasse 7, D-38124 Braunschweig, Germany
| | - Michael Morr
- Department of Vaccinology and Applied Microbiology, Helmholtz Centre of Infection Research, Inhoffenstrasse 7, D-38124 Braunschweig, Germany
| | - Carlos A Guzmán
- Department of Vaccinology and Applied Microbiology, Helmholtz Centre of Infection Research, Inhoffenstrasse 7, D-38124 Braunschweig, Germany
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64
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Schirmer T, Jenal U. Structural and mechanistic determinants of c-di-GMP signalling. Nat Rev Microbiol 2009; 7:724-35. [PMID: 19756011 DOI: 10.1038/nrmicro2203] [Citation(s) in RCA: 374] [Impact Index Per Article: 24.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Bis-(3'-5')-cyclic dimeric GMP (c-di-GMP) is a ubiquitous second messenger that regulates cell surface-associated traits in bacteria. Components of this regulatory network include GGDEF and EAL domain-containing proteins that determine the cellular concentrations of c-di-GMP by mediating its synthesis and degradation, respectively. Crystal structure analyses in combination with functional studies have revealed the catalytic mechanisms and regulatory principles involved. Downstream, c-di-GMP is recognized by PilZ domain-containing receptors that can undergo large-scale domain rearrangements on ligand binding. Here, we review recent data on the structure and functional properties of the protein families that are involved in c-di-GMP signalling and discuss the mechanistic implications.
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Affiliation(s)
- Tilman Schirmer
- Biozentrum, University of Basel, Klingelbergstrasse 50, CH-4056 Basel, Switzerland.
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65
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Yan H, KuoLee R, Tram K, Qiu H, Zhang J, Patel GB, Chen W. 3',5'-Cyclic diguanylic acid elicits mucosal immunity against bacterial infection. Biochem Biophys Res Commun 2009; 387:581-4. [PMID: 19615973 DOI: 10.1016/j.bbrc.2009.07.061] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2009] [Accepted: 07/14/2009] [Indexed: 12/30/2022]
Abstract
3',5'-Cyclic diguanylic acid (cdiGMP) is emerging as a universal bacterial second messenger in regulating bacterial growth on surfaces. It has been recently shown that cdiGMP stimulates innate immunity and enhances antigen-specific humoral and cellular immune responses. We herein report that intranasal (i.n.) administration with cdiGMP induces an acute but transient inflammatory response and activation of dendritic cells in the lungs. Moreover, i.n. immunization of mice with pneumococcal surface adhesion A (PsaA) in conjunction with cdiGMP elicited strong antigen-specific serum immunoglobulin G (IgG) and secretory IgA antibody responses at multiple mucosal surfaces. More importantly, the immunized mice showed significantly reduced nasopharyngeal Streptococcus pneumoniae colonization. These results, for the first time, provide direct evidence for the induction of protection against mucosal bacterial infections by cdiGMP as an adjuvant.
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Affiliation(s)
- Hongbin Yan
- Department of Chemistry, Brock University, St. Catharines, Ontario, Canada.
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66
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c-di-GMP as a vaccine adjuvant enhances protection against systemic methicillin-resistant Staphylococcus aureus (MRSA) infection. Vaccine 2009; 27:4867-73. [PMID: 19406185 DOI: 10.1016/j.vaccine.2009.04.053] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2009] [Revised: 04/11/2009] [Accepted: 04/20/2009] [Indexed: 11/22/2022]
Abstract
Cyclic diguanylate (c-di-GMP) is a novel immunomodulator and immune enhancer that triggers a protective host innate immune response. The protective effect of c-di-GMP as a vaccine adjuvant against Staphylococcus aureus infection was investigated by subcutaneous (s.c.) vaccination with two different S. aureus antigens, clumping factor A (ClfA) and a nontoxic mutant staphylococcal enterotoxin C (mSEC), then intravenous (i.v.) challenge with viable methicillin-resistant S. aureus (MRSA) in a systemic infection model. Mice immunized with c-di-GMP plus mSEC or c-di-GMP plus ClfA vaccines then challenged with MRSA produced strong antigen-specific antibody responses demonstrating immunogenicity of the vaccines. Bacterial counts in the spleen and liver of c-di-GMP plus mSEC and c-di-GMP plus ClfA-immunized mice were significantly lower than those of control mice (P<0.001). Mice immunized with c-di-GMP plus mSEC or c-di-GMP plus ClfA showed significantly higher survival rates at day 7 (87.5%) than those of the non-immunized control mice (33.3%) (P<0.05). Furthermore, immunization of mice with c-di-GMP plus mSEC or c-di-GMP plus ClfA induced not only very high titers of immunoglobulin G1 (IgG1), but c-di-GMP plus mSEC also induced significantly higher levels of IgG2a, IgG2b and IgG3 compared to alum adjuvant (P<0.01 and P<0.001, respectively) and c-di-GMP plus ClfA induced significantly higher levels of IgG2a, IgG2b and IgG3 compared to alum adjuvant (P<0.001). Our results show that c-di-GMP should be developed as an adjuvant and immunotherapeutic to provide protection against systemic infection caused by S. aureus (MRSA).
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