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Zhou G, Zhao Y, Ma Q, Li Q, Wang S, Shi H. Manipulation of host immune defenses by effector proteins delivered from multiple secretion systems of Salmonella and its application in vaccine research. Front Immunol 2023; 14:1152017. [PMID: 37081875 PMCID: PMC10112668 DOI: 10.3389/fimmu.2023.1152017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2023] [Accepted: 03/23/2023] [Indexed: 04/07/2023] Open
Abstract
Salmonella is an important zoonotic bacterial species and hazardous for the health of human beings and livestock globally. Depending on the host, Salmonella can cause diseases ranging from gastroenteritis to life-threatening systemic infection. In this review, we discuss the effector proteins used by Salmonella to evade or manipulate four different levels of host immune defenses: commensal flora, intestinal epithelial-mucosal barrier, innate and adaptive immunity. At present, Salmonella has evolved a variety of strategies against host defense mechanisms, among which various effector proteins delivered by the secretory systems play a key role. During its passage through the digestive system, Salmonella has to face the intact intestinal epithelial barrier as well as competition with commensal flora. After invasion of host cells, Salmonella manipulates inflammatory pathways, ubiquitination and autophagy processes with the help of effector proteins. Finally, Salmonella evades the adaptive immune system by interfering the migration of dendritic cells and interacting with T and B lymphocytes. In conclusion, Salmonella can manipulate multiple aspects of host defense to promote its replication in the host.
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Affiliation(s)
- Guodong Zhou
- College of Veterinary Medicine, Yangzhou University, Yangzhou, Jiangsu, China
- Jiangsu Co-innovation Center for the Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, China
| | - Yuying Zhao
- College of Veterinary Medicine, Yangzhou University, Yangzhou, Jiangsu, China
- Jiangsu Co-innovation Center for the Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, China
| | - Qifeng Ma
- College of Veterinary Medicine, Yangzhou University, Yangzhou, Jiangsu, China
- Jiangsu Co-innovation Center for the Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, China
| | - Quan Li
- College of Veterinary Medicine, Yangzhou University, Yangzhou, Jiangsu, China
- Jiangsu Co-innovation Center for the Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, China
| | - Shifeng Wang
- Department of Infectious Diseases and Immunology, College of Veterinary Medicine, University of Florida, Gainesville, FL, United States
| | - Huoying Shi
- College of Veterinary Medicine, Yangzhou University, Yangzhou, Jiangsu, China
- Jiangsu Co-innovation Center for the Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, China
- Joint International Research Laboratory of Agriculture and Agri-Product Safety, Yangzhou University (JIRLAAPS), Yangzhou, China
- *Correspondence: Huoying Shi,
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Agbayani G, Clark K, Sad S, Murphy SP, Krishnan L. Roles of natural resistance-associated macrophage protein-1 in modulating bacterial distribution and immune responses during Salmonella enterica serovar Typhimurium infection in murine pregnancy. Am J Reprod Immunol 2022; 88:e13599. [PMID: 35851978 PMCID: PMC9509426 DOI: 10.1111/aji.13599] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2022] [Revised: 06/23/2022] [Accepted: 07/05/2022] [Indexed: 11/27/2022] Open
Abstract
PROBLEM Salmonella enterica serovar Typhimurium (S.Tm) infection in Nramp1+/+ mice during pregnancy can lead to profound bacterial growth in the feto-placental unit and adverse pregnancy outcomes, including fetal loss, maternal illness and death. The kinetics and mechanisms by which S.Tm gains entry within individual feto-placental unit, and disseminates through tissues leading to placental resorption and fetal demise remain unclear. METHOD OF STUDY Mice were systemically infected with S.Tm. Bacterial burden within spleen and individual placentas, and placental/fetal resorptions were quantified. Flow cytometric analysis of immune cell types in the spleen and individual placentas was performed. Cytokine expression in maternal serum was determined through cytometric bead array. RESULTS Systemic infection with S.Tm resulted in preferential bacterial proliferation in placentas compared to the spleen in Nramp1+/+ mice. At 24 h post-infection, the mean infection rate of individual placentas per mouse was ∼50%, increasing to >75% by 72 h post-infection, suggesting that initial infection in few sites progresses to rapid spread of infection through the uterine milieu. This correlated with a steady increase in placental/fetal resorption rates. Placental infection was associated with local increased neutrophil percentages, whereas numbers and percentages in the spleen remained unchanged, suggesting dichotomous modulation of inflammation between the systemic compartment and the feto-maternal interface. Reduced survival rates of pregnant mice during infection correlated with decreased serum IFN-γ but increased IL-10 levels relative to non-pregnant controls. CONCLUSION Pregnancy compromises host resistance conferred by Nramp1 against S.Tm through compartment-specific regulation of maternal and placental cellular responses, and modulation of systemic cytokine expression.
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Affiliation(s)
- Gerard Agbayani
- Division of Life Sciences, Human Health Therapeutics, National Research Council Canada, Ottawa, Ontario, Canada
| | - Kristina Clark
- Division of Life Sciences, Human Health Therapeutics, National Research Council Canada, Ottawa, Ontario, Canada
| | - Subash Sad
- Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Ontario, Canada
| | - Shawn P Murphy
- Department of Obstetrics and Gynecology, University of Rochester, Rochester, New York, USA
- Department of Microbiology and Immunology, University of Rochester, Rochester, New York, USA
| | - Lakshmi Krishnan
- Division of Life Sciences, Human Health Therapeutics, National Research Council Canada, Ottawa, Ontario, Canada
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Praveen C, Bhatia SS, Alaniz RC, Droleskey RE, Cohen ND, Jesudhasan PR, Pillai SD. Assessment of microbiological correlates and immunostimulatory potential of electron beam inactivated metabolically active yet non culturable (MAyNC) Salmonella Typhimurium. PLoS One 2021; 16:e0243417. [PMID: 33861743 PMCID: PMC8051754 DOI: 10.1371/journal.pone.0243417] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2019] [Accepted: 11/23/2020] [Indexed: 12/02/2022] Open
Abstract
This study investigates the microbiological and immunological basis underlying the efficacy of electron beam-inactivated immune modulators. The underlying hypothesis is that exposure to eBeam-based ionization reactions inactivate microorganisms without modifying their antigenic properties and thereby creating immune modulators. The immunological correlates of protection induced by such eBeam based Salmonella Typhimurium (EBST) immune modulators in dendritic cell (DC) (in vitro) and mice (in vivo) models were assessed. The EBST stimulated innate pro inflammatory response (TNFα) and maturation (MHC-II, CD40, CD80 and CD86) of DC. Immuno-stimulatory potential of EBST was on par with both a commercial Salmonella vaccine, and live Salmonella cells. The EBST cells did not multiply under permissive in vitro and in vivo conditions. However, EBST cells remained metabolically active. EBST immunized mice developed Salmonella-specific CD4+ T-cells that produced the Th1 cytokine IFNγ at a level similar to that induced by the live attenuated vaccine (AroA- ST) formulation. The EBST retained stable immunogenic properties for several months at room temperature, 4°C, and -20°C as well as after lyophilization. Therefore, such eBeam-based immune modulators have potential as vaccine candidates since they offer the safety of a “killed” vaccine, while retaining the immunogenicity of an “attenuated” vaccine. The ability to store eBeam based immune modulators at room temperature without loss of potency is also noteworthy.
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Affiliation(s)
- Chandni Praveen
- National Center for Electron Beam Research-an International Atomic Energy Agency (IAEA) Collaborating Centre for Electron Beam Technology, Texas A&M University, College Station, TX, United States of America
| | - Sohini S. Bhatia
- National Center for Electron Beam Research-an International Atomic Energy Agency (IAEA) Collaborating Centre for Electron Beam Technology, Texas A&M University, College Station, TX, United States of America
| | - Robert C. Alaniz
- Department of Microbial Pathogenesis and Immunology, Texas A&M University Health Science Center, College Station, TX, United States of America
- * E-mail: (SDP); (RCA)
| | - Robert E. Droleskey
- Food and Feed Safety Research Unit, Southern Plains Agricultural Research Center, USDA-ARS, College Station, TX, United States of America
| | - Noah D. Cohen
- Department of Large Animal Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, United States of America
| | - Palmy R. Jesudhasan
- Poultry Production and Product Safety, USDA-ARS, University of Arkansas, Fayetteville, AR, United States of America
| | - Suresh D. Pillai
- National Center for Electron Beam Research-an International Atomic Energy Agency (IAEA) Collaborating Centre for Electron Beam Technology, Texas A&M University, College Station, TX, United States of America
- * E-mail: (SDP); (RCA)
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A Salmonella typhimurium ghost vaccine induces cytokine expression in vitro and immune responses in vivo and protects rats against homologous and heterologous challenges. PLoS One 2017; 12:e0185488. [PMID: 28961267 PMCID: PMC5621678 DOI: 10.1371/journal.pone.0185488] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2017] [Accepted: 09/13/2017] [Indexed: 01/13/2023] Open
Abstract
Salmonella enteritidis and Salmonella typhimurium are important food-borne bacterial pathogens, which are responsible for diarrhea and gastroenteritis in humans and animals. In this study, S. typhimurium bacterial ghost (STG) was generated based on minimum inhibitory concentration (MIC) of sodium hydroxide (NaOH). Experimental studies performed using in vitro and in vivo experimental model systems to characterize effects of STG as a vaccine candidate. When compared with murine macrophages (RAW 264.7) exposed to PBS buffer (98.1%), the macrophages exposed to formalin-killed inactivated cells (FKC), live wild-type bacterial cells and NaOH-induced STG at 1 × 108 CFU/mL showed 85.6%, 66.5% and 84.6% cell viability, respectively. It suggests that STG significantly reduces the cytotoxic effect of wild-type bacterial cells. Furthermore, STG is an excellent inducer for mRNAs of pro-inflammatory cytokine (TNF-α, IL-1β) and factor (iNOS), anti-inflammatory cytokine (IL-10) and dual activities (IL-6) in the stimulated macrophage cells. In vivo, STG vaccine induced humoral and cellular immune responses and protection against homologous and heterologous challenges in rats. Furthermore, the immunogenicity and protective efficacy of STG vaccine were compared with those of FKC and non-vaccinated PBS control groups. The vaccinated rats from STG group exhibited higher levels of serum IgG antibody responses, serum bactericidal antibodies, and CD4+ and CD8+ T-cell populations than those of the FKC and PBS control groups. Most importantly, after challenge with homologous and heterologous strains, the bacterial loads in the STG group were markedly lower than the FKC and PBS control groups. In conclusion, these findings suggest that the STG vaccine induces protective immunity against homologous and heterologous challenges.
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Abstract
The best-characterized mucosa-associated lymphoid tissue (MALT), and also the most relevant for this review, is the gastrointestinal-associated lymphoid tissue (GALT). The review reviews our understanding of the importance of mucosal immune responses in resisting infections caused by E. coli and Salmonella spp. It focuses on the major human E. coli infections and discusses whether antigen-specific mucosal immune responses are important for resistance against primary infection or reinfection by pathogenic E. coli. It analyzes human data on mucosal immunity against E. coli, a growing body of data of mucosal responses in food production animals and other natural hosts of E. coli, and more recent experimental studies in mice carrying defined deletions in genes encoding specific immunological effectors, to show that there may be considerable conservation of the effective host mucosal immune response against this pathogen. The species Salmonella enterica contains a number of serovars that include pathogens of both humans and animals; these bacteria are frequently host specific and may cause different diseases in different hosts. Ingestion of various Salmonella serovars, such as Typhimurium, results in localized infections of the small intestine leading to gastroenteritis in humans, whereas ingestion of serovar Typhi results in systemic infection and enteric fever. Serovar Typhi infects only humans, and the review discusses the mucosal immune responses against serovar Typhi, focusing on the responses in humans and in the mouse typhoid fever model.
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Lopez-Medina M, Perez-Lopez A, Alpuche-Aranda C, Ortiz-Navarrete V. Salmonella modulates B cell biology to evade CD8(+) T cell-mediated immune responses. Front Immunol 2014; 5:586. [PMID: 25484884 PMCID: PMC4240163 DOI: 10.3389/fimmu.2014.00586] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2014] [Accepted: 11/03/2014] [Indexed: 12/22/2022] Open
Abstract
Although B cells and antibodies are the central effectors of humoral immunity, B cells can also produce and secrete cytokines and present antigen to helper T cells. The uptake of antigen is mainly mediated by endocytosis; thus, antigens are often presented by MHC-II molecules. However, it is unclear if B cells can present these same antigens via MHC-I molecules. Recently, Salmonella bacteria were found to infect B cells, allowing possible antigen cross-processing that could generate bacterial peptides for antigen presentation via MHC-I molecules. Here, we will discuss available knowledge regarding Salmonella antigen presentation by infected B cell MHC-I molecules and subsequent inhibitory effects on CD8(+) T cells for bacterial evasion of cell-mediated immunity.
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Affiliation(s)
- Marcela Lopez-Medina
- Departamento de Biomedicina Molecular, Centro de Investigación y Estudios Avanzados del IPN , México City, DF , Mexico
| | - Araceli Perez-Lopez
- Department of Microbiology and Molecular Genetics, Irvine School of Medicine, University of California , Irvine, CA , USA
| | - Celia Alpuche-Aranda
- Instituto Nacional de Salud Pública, Secretaría de Salud y Asistencia , Cuernavaca, Morelos CP , Mexico
| | - Vianney Ortiz-Navarrete
- Departamento de Biomedicina Molecular, Centro de Investigación y Estudios Avanzados del IPN , México City, DF , Mexico
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Systems biology approaches for understanding cellular mechanisms of immunity in lymph nodes during infection. J Theor Biol 2011; 287:160-70. [PMID: 21798267 DOI: 10.1016/j.jtbi.2011.06.037] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2011] [Revised: 06/30/2011] [Accepted: 06/30/2011] [Indexed: 12/20/2022]
Abstract
Adaptive immunity is initiated in secondary lymphoid tissues when naive T cells recognize foreign antigen presented as MHC-bound peptide on the surface of dendritic cells. Only a small fraction of T cells in the naive repertoire will express T cell receptors specific for a given epitope, but antigen recognition triggers T cell activation and proliferation, thus greatly expanding antigen-specific clones. Expanded T cells can serve a helper function for B cell responses or traffic to sites of infection to secrete cytokines or kill infected cells. Over the past decade, two-photon microscopy of lymphoid tissues has shed important light on T cell development, antigen recognition, cell trafficking and effector functions. These data have enabled the development of sophisticated quantitative and computational models that, in turn, have been used to test hypotheses in silico that would otherwise be impossible or difficult to explore experimentally. Here, we review these models and their principal findings and highlight remaining questions where modeling approaches are poised to advance our understanding of complex immunological systems.
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Lahiri A, Lahiri A, Das P, Vani J, Shaila MS, Chakravortty D. TLR 9 activation in dendritic cells enhances salmonella killing and antigen presentation via involvement of the reactive oxygen species. PLoS One 2010; 5:e13772. [PMID: 21048937 PMCID: PMC2966436 DOI: 10.1371/journal.pone.0013772] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2010] [Accepted: 10/12/2010] [Indexed: 11/19/2022] Open
Abstract
Synthetic CpG containing oligodeoxynucleotide Toll like receptor-9 agonist (CpG DNA) activates innate immunity and can stimulate antigen presentation against numerous intracellular pathogens. It was observed that Salmonella Typhimurium growth can be inhibited by the CpG DNA treatment in the murine dendritic cells. This inhibitory effect was mediated by an increased reactive oxygen species production. In addition, it was noted that CpG DNA treatment of dendritic cells during Salmonella infection leads to an increased antigen presentation. Further this increased antigen presentation was dependent on the enhanced reactive oxygen species production elicited by Toll like receptor-9 activation. With the help of an exogenous antigen it was shown that Salmonella antigen could also be cross-presented in a better way by CpG induction. These data collectively indicate that CpG DNA enhance the ability of murine dendritic cells to contain the growth of virulent Salmonella through reactive oxygen species dependent killing.
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Affiliation(s)
- Amit Lahiri
- Center for Infectious Disease Research and Biosafety Laboratories, Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
| | - Ayan Lahiri
- Center for Infectious Disease Research and Biosafety Laboratories, Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
| | - Priyanka Das
- Center for Infectious Disease Research and Biosafety Laboratories, Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
| | - Janakiraman Vani
- Center for Infectious Disease Research and Biosafety Laboratories, Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
| | - M. S. Shaila
- Center for Infectious Disease Research and Biosafety Laboratories, Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
| | - Dipshikha Chakravortty
- Center for Infectious Disease Research and Biosafety Laboratories, Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
- * E-mail:
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Linderman JJ, Riggs T, Pande M, Miller M, Marino S, Kirschner DE. Characterizing the dynamics of CD4+ T cell priming within a lymph node. THE JOURNAL OF IMMUNOLOGY 2010; 184:2873-85. [PMID: 20154206 DOI: 10.4049/jimmunol.0903117] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Generating adaptive immunity postinfection or immunization requires physical interaction within a lymph node T zone between Ag-bearing dendritic cells (DCs) and rare cognate T cells. Many fundamental questions remain regarding the dynamics of DC-CD4+ T cell interactions leading to priming. For example, it is not known how the production of primed CD4+ T cells relates to the numbers of cognate T cells, Ag-bearing DCs, or peptide-MHCII level on the DC. To address these questions, we developed an agent-based model of a lymph node to examine the relationships among cognate T cell frequency, DC density, parameters characterizing DC-T cell interactions, and the output of primed T cells. We found that the output of primed CD4+ T cells is linearly related to cognate frequency, but nonlinearly related to the number of Ag-bearing DCs present during infection. This addresses the applicability of two photon microscopy studies to understanding actual infection dynamics, because these types of experiments increase the cognate frequency by orders of magnitude compared with physiologic levels. We found a trade-off between the quantity of peptide-major histocompatibility class II on the surface of individual DCs and number of Ag-bearing DCs present in the lymph node in contributing to the production of primed CD4+ T cells. Interestingly, peptide-major histocompatibility class II t(1/2) plays a minor, although still significant, role in determining CD4+ T cell priming, unlike the primary role that has been suggested for CD8+ T cell priming. Finally, we identify several pathogen-targeted mechanisms that, if altered in their efficiency, can significantly effect the generation of primed CD4+ T cells.
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Affiliation(s)
- Jennifer J Linderman
- Department of Chemical Engineering, Center for Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, MI 48109, USA
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Mittal R, Prasadarao NV. Outer Membrane Protein A Expression inEscherichia coliK1 Is Required to Prevent the Maturation of Myeloid Dendritic Cells and the Induction of IL-10 and TGF-β. THE JOURNAL OF IMMUNOLOGY 2008; 181:2672-82. [DOI: 10.4049/jimmunol.181.4.2672] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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Trülzsch K, Sporleder T, Leibiger R, Rüssmann H, Heesemann J. Yersinia as oral live carrier vaccine: influence of Yersinia outer proteins (Yops) on the T-cell response. Int J Med Microbiol 2007; 298:59-67. [PMID: 17897880 DOI: 10.1016/j.ijmm.2007.08.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Attenuated enteropathogenic Yersinia strains are attractive candidates for the development of oral live carrier vaccines. Yersiniae colonize the small intestine and invade lymphoid tissue of the terminal ileum where they replicate extracellularly. Yersiniae can be engineered to secrete or translocate heterologous antigens into the cytosol of antigen-presenting cells by their type 3 secretion system (T3SS). This results in the induction of both cellular and humoral immune responses to heterologous antigens of viral, bacterial and parasitic origin. In this review, we summarize the progress in developing Yersinia-based vaccine carrier strains by mutating the T3SS effector proteins of Yersinia called Yops (Yersinia outer proteins) to both attenuate the strains and to modulate the T-cell response.
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Affiliation(s)
- Konrad Trülzsch
- Max von Pettenkofer-Institut, LMU München, Pettenkoferstr. 9a, D-80336 München, Germany.
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Eguchi M, Sekiya Y, Kikuchi Y, Takaya A, Yamamoto T, Matsui H. ExpressedSalmonellaantigens within macrophages enhance the proliferation of CD4+and CD8+T lymphocytes by means of bystander dendritic cells. ACTA ACUST UNITED AC 2007; 50:411-20. [PMID: 17573927 DOI: 10.1111/j.1574-695x.2007.00275.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
ATP-dependent Lon protease-deficient Salmonella enterica serovar Typhimurium (strain CS2022) appeared to invade successfully the mesenteric lymph nodes (MLN) and Peyer's patches (PP) of BALB/c mice and appeared to be easily eradicated by the host after oral immunization. As detected by flow cytometry, the population of major histocompatibility complex class I (MHC-I)-expressing macrophages and dendritic cells (DCs) was increased in the PP of mice immunized with CS2022 on day 6 after immunization. Thereafter, the population of splenic surface CD69(+) T lymphocytes prepared from mice immunized with CS2022 6 weeks prior to measurement increased as a result of the administration of the extracellular vesicles of RAW264.7 macrophage-like cells derived by Salmonella challenge. In addition, the proliferation of CD8(+) and even of CD4(+)T cells isolated from mouse spleens immunized with CS2022 was enhanced after cocultivation with naive DCs in the presence of the extracellular vesicles. These findings indicate that the extracellular vesicles prepared from the Salmonella-challenged macrophages carried salmonellae antigens to bystander DCs, thereby stimulating T-cell responses. Therefore, as antigen presentation after phagocytosis should be a central process in the T-cell activation that occurs in response to Salmonella infection, an oral immunization with CS2022 sufficiently induces T cell-mediated immunity in mice.
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Affiliation(s)
- Masahiro Eguchi
- Kitasato Institute for Life Sciences and Graduate School of Infection Control Sciences, Kitasato University, Tokyo, Japan
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Carreño LJ, Bueno SM, Bull P, Nathenson SG, Kalergis AM. The half-life of the T-cell receptor/peptide-major histocompatibility complex interaction can modulate T-cell activation in response to bacterial challenge. Immunology 2007; 121:227-37. [PMID: 17313485 PMCID: PMC2265936 DOI: 10.1111/j.1365-2567.2007.02561.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
T-cell activation results from engagement of the T-cell receptor (TCR) by cognate peptide-major histocompatibility complex (pMHC) complexes on the surface of antigen-presenting cells (APC). Previous studies have provided evidence supporting the notion that the half-life of the TCR/pMHC interaction and the density of pMHC on the APC are two parameters that can influence T-cell activation. However, whether the half-life of the TCR/pMHC interaction can modulate T-cell activation in response to a pathogen challenge remains unknown. To approach this question, we generated strains of bacteria expressing variants of the ovalbumin (OVA) antigen, carrying point mutations in the SIINFEKL sequence. When bound to H-2K(b), this peptide is the cognate ligand for the OT-I TCR. Variants of the H-2K(b)/SIINFEKL bind to the OT-I TCR with distinct half-lives. Here we show that dendritic cells (DCs) infected with bacteria expressing OVA variants were incapable of activating OT-I T cells when the half-life of the TCR/H-2K(b)/OVA interaction was excessively short. Consistent with these data, T-cell activation was only observed in mice infected with bacteria expressing OVA variants that bound to OT-I with a half-life above a certain threshold. Considered together, our data suggest that the half-life of TCR/pMHC interaction can significantly modulate T-cell activation in vivo, as well as influence recognition of antigens expressed by bacteria. These observations underscore the importance of the TCR/pMHC half-life on the clearance of pathogens.
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Affiliation(s)
- Leandro J Carreño
- Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile
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Zhao C, Wood MW, Galyov EE, Höpken UE, Lipp M, Bodmer HC, Tough DF, Carter RW. Salmonella typhimurium infection triggers dendritic cells and macrophages to adopt distinct migration patterns in vivo. Eur J Immunol 2007; 36:2939-50. [PMID: 17048271 DOI: 10.1002/eji.200636179] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The presence of an anti-bacterial T cell response and evidence of bacterial products in inflamed joints of reactive arthritis patients suggests an antigen transportation role in this disease for macrophages and dendritic cells. We have investigated the functional properties and in vivo migration of macrophages and DC after infection with Salmonella enterica serovar Typhimurium (S. typhimurium). BM-derived macrophages and DC displayed enhanced expression of costimulatory molecules (CD40 and CD86) and increased production of pro-inflammatory cytokines (TNF-alpha, IL-6 and IL-12p40) and nitric oxide after infection. Upon adoptive transfer into mice, infected DC migrated to lymphoid tissues and induced an anti-Salmonella T cell response, whereas infected macrophages did not. Infection of DC with S. typhimurium was associated with strong up-regulation of the chemokine receptor CCR7 and acquisition of responsiveness to chemokines acting through this receptor. Moreover, S. typhimurium-infected CCR7-deficient DC were unable to migrate to lymph nodes after adoptive transfer, although they did reach the spleen. Our data demonstrate distinct roles for macrophages and DC as antigen transporters after S. typhimurium infection and a dependence on CCR7 for migration of DC to lymph nodes after bacterial infection.
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Affiliation(s)
- Chunfang Zhao
- The Edward Jenner Institute for Vaccine Research, Compton, Newbury, UK
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Tobar JA, Carreño LJ, Bueno SM, González PA, Mora JE, Quezada SA, Kalergis AM. Virulent Salmonella enterica serovar typhimurium evades adaptive immunity by preventing dendritic cells from activating T cells. Infect Immun 2006; 74:6438-48. [PMID: 17057096 PMCID: PMC1695529 DOI: 10.1128/iai.00063-06] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Dendritic cells (DCs) constitute the link between innate and adaptive immunity by directly recognizing pathogen-associated molecular patterns (PAMPs) in bacteria and by presenting bacterial antigens to T cells. Recognition of PAMPs renders DCs as professional antigen-presenting cells able to prime naïve T cells and initiate adaptive immunity against bacteria. Therefore, interfering with DC function would promote bacterial survival and dissemination. Understanding the molecular mechanisms that have evolved in virulent bacteria to evade activation of adaptive immunity requires the characterization of virulence factors that interfere with DC function. Salmonella enterica serovar Typhimurium, the causative agent of typhoid-like disease in the mouse, can prevent antigen presentation to T cells by avoiding lysosomal degradation in DCs. Here, we show that this feature of virulent Salmonella applies in vivo to prevent activation of adaptive immunity. In addition, this attribute of virulent Salmonella requires functional expression of a type three secretion system (TTSS) and effector proteins encoded within the Salmonella pathogenicity island 2 (SPI-2). In contrast to wild-type virulent Salmonella, mutant strains carrying specific deletions of SPI-2 genes encoding TTSS components or effectors proteins are targeted to lysosomes and are no longer able to prevent DCs from activating T cells in vitro or in vivo. SPI-2 mutant strains are attenuated in vivo, showing reduced tissue colonization and enhanced T-cell activation, which confers protection against a challenge with wild-type virulent Salmonella. Our data suggest that impairment of DC function by the activity of SPI-2 gene products is crucial for Salmonella pathogenesis.
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Affiliation(s)
- Jaime A Tobar
- Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Alameda #340, Santiago, Chile
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Fu G, Wijburg OLC, Cameron PU, Price JD, Strugnell RA. Salmonella enterica Serovar Typhimurium infection of dendritic cells leads to functionally increased expression of the macrophage-derived chemokine. Infect Immun 2005; 73:1714-22. [PMID: 15731072 PMCID: PMC1064904 DOI: 10.1128/iai.73.3.1714-1722.2005] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Gene expression in murine dendritic cells (DCs) infected with green fluorescent protein-expressing Salmonella enterica serovar Typhimurium BRD509 was studied by mRNA differential display. Infected DCs were sorted from uninfected cells by flow cytometry. The mRNA expression patterns of infected and uninfected cells revealed a number of differentially expressed transcripts, which included the macrophage-derived chemokine (MDC). Up-regulation of MDC transcription in infected DCs was confirmed by Northern blotting, and the kinetics of MDC expression was examined by real-time reverse transcription-PCR, with which 31- and 150-fold increases were detected at 2 and 6 h postinfection, respectively. The increased release by DCs of MDC into culture media was detected by an enzyme-linked immunosorbent assay. The biological activity of MDC was investigated in in vitro and in vivo assays. In vitro, supernatants from S. enterica serovar Typhimurium-infected DCs were chemoattractive to T cells, and neutralization of MDC in these supernatants inhibited T-cell migration. Passive transfer of anti-MDC antibody to mice infected with BRD509 revealed that neither growth of the bacterium nor resistance of the mice to reinfection was affected and that in vivo inhibition of MDC did not affect T-cell responses, as measured by the gamma interferon ELISPOT method 3 days after challenge infection.
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Affiliation(s)
- Guo Fu
- CRC for Vaccine Technology, Parkville, Victoria 3010, Australia
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18
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Trülzsch K, Geginat G, Sporleder T, Ruckdeschel K, Hoffmann R, Heesemann J, Rüssmann H. YersiniaOuter Protein P Inhibits CD8 T Cell Priming in the Mouse Infection Model. THE JOURNAL OF IMMUNOLOGY 2005; 174:4244-51. [DOI: 10.4049/jimmunol.174.7.4244] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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19
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Reimund JM, Muller CD, Finck G, Escalin G, Duclos B, Baumann R. Factors contributing to infectious diarrhea-associated pancreatic enzyme alterations. ACTA ACUST UNITED AC 2005; 29:247-53. [PMID: 15864174 DOI: 10.1016/s0399-8320(05)80757-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
OBJECTIVES Several pathogens have been involved as etiologic agents of acute pancreatitis. We studied 59 patients presenting acute infectious diarrhea in order to determine the incidence as well as to identify factors which may contribute to the occurrence of pancreatic enzyme alteration or true acute pancreatitis. METHODS Patients were evaluated for serum lipase and amylase, and 24-hours urinary amylase. Clinical and biological parameters were noted. Abdominal sonography and rectosigmoidoscopy were performed. RESULTS Pancreatic enzyme alteration was found in 24% of patients. Twelve had salmonellosis and 2 Campylobacter jejuni infection. They had more prolonged diarrhea, more frequent renal impairment and increased triglyceridemia. Triglyceridemia was correlated to blood amylase, inflammatory syndrome and renal impairment. Serum amylase was linked to serum urea and creatinine and to biological markers of inflammation. Three patients had true acute pancreatitis. CONCLUSION Patients presenting dysentery-like infectious diarrhea and upper abdominal pain should be investigated for concomitant pancreatic reaction or acute pancreatitis which seems more frequent in patients with enterocolitis due to enteroinvasive microbes, mostly non-typhoidal Salmonella. Pancreatic disturbances are related to the severity of these infections. However, overt infectious diarrhea-associated pancreatitis is a rare event.
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Affiliation(s)
- Jean-Marie Reimund
- Service d'Hépato-Gastroentérologie et d'Assistance Nutritive, Hôpitaux Universitaires de Strasbourg, Hôpital de Hautepierre, Avenue Molière, 67098 Strasbourg Cedex.
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20
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Mucosal Immunity to Bacteria. Mucosal Immunol 2005. [DOI: 10.1016/b978-012491543-5/50046-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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21
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Tobar JA, González PA, Kalergis AM. SalmonellaEscape from Antigen Presentation Can Be Overcome by Targeting Bacteria to Fcγ Receptors on Dendritic Cells. THE JOURNAL OF IMMUNOLOGY 2004; 173:4058-65. [PMID: 15356155 DOI: 10.4049/jimmunol.173.6.4058] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Dendritic cells (DCs) are professional APCs with the unique ability to activate naive T cells, which is required for initiation of the adaptive immune response against pathogens. Therefore, interfering with DC function would be advantageous for pathogen survival and dissemination. In this study we provide evidence suggesting that Salmonella enterica serovar typhimurium, the causative agent of typhoid disease in the mouse, interferes with DC function. Our results indicate that by avoiding lysosomal degradation, S. typhimurium impairs the ability of DCs to present bacterial Ags on MHC class I and II molecules to T cells. This process could correspond to a novel mechanism developed by this pathogen to evade adaptive immunity. In contrast, when S. typhimurium is targeted to FcgammaRs on DCs by coating bacteria with Salmonella-specific IgG, bacterial Ags are efficiently processed and presented on MHC class I and class II molecules. This enhanced Ag presentation leads to a robust activation of bacteria-specific T cells. Laser confocal microscopy experiments show that virulent S. typhimurium is rerouted to the lysosomal degradation pathway of DCs when internalized through FcgammaR. These observations are supported by electron microscopy studies demonstrating that internalized S. typhimurium shows degradation signs only when coated with IgG and captured by FcgammaRs on DCs. Therefore, our data support a potential role for bacteria-specific IgG on the augmentation of Ag processing and presentation by DCs to T cells during the immune response against intracellular bacteria.
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Affiliation(s)
- Jaime A Tobar
- Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile
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22
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Cooke A, Zaccone P, Raine T, Phillips JM, Dunne DW. Infection and autoimmunity: are we winning the war, only to lose the peace? Trends Parasitol 2004; 20:316-21. [PMID: 15193562 DOI: 10.1016/j.pt.2004.04.010] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Affiliation(s)
- Anne Cooke
- Pathology Department, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK.
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23
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Winau F, Kaufmann SHE, Schaible UE. Apoptosis paves the detour path for CD8 T cell activation against intracellular bacteria. Cell Microbiol 2004; 6:599-607. [PMID: 15186397 DOI: 10.1111/j.1462-5822.2004.00408.x] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Intracellular bacteria such as Mycobacterium tuberculosis primarily infect macrophages. Within these host cells, the pathogens are confined to phagosomes and their antigens are secluded from the classical MHC I presentation pathway. Moreover, macrophages fail to express certain antigen presenting molecules like CD1 proteins. As a result of this intracellular lifestyle, the pathways for the induction of MHC I- and CD1-restricted CD8 T cells by such microorganisms remain elusive. Based on recent findings in tuberculosis and salmonellosis, we propose a new detour pathway for CD8 T cell activation against intracellular bacteria through apoptotic blebs from infected macrophages. Pathogen-derived antigens including proteins and lipids are delivered from infected cells to non-infected dendritic cells. Subsequently, these professional antigen presenting cells display microbial antigens through MHC I and CD1 to T cells. Thus, cross-priming mediated by apoptotic vesicles is not just a matter of antigen distribution, but an intrinsic immunological function due to the nature of phagosomally located intracellular bacteria. We consider infection-induced apoptosis the conditio sine qua non for antigen-specific CD8 T cell activation by phagosome-enclosed pathogens. This important new function of cell death in antibacterial immunity requires consideration for rational vaccine design.
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Affiliation(s)
- Florian Winau
- Max-Planck-Institute for Infection Biology, Department of Immunology, Schumannstr. 21-22, D-10117 Berlin, Germany
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24
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Abstract
Dendritic cells (DC) are the key link between innate and adaptive immunity. Features of DC, including their presence at sites of antigen entry, their ability to migrate from peripheral sites to secondary lymphoid organs, and their superior capacity to stimulate naïve T cells places them in this pivotal role in the immune system. DC also produce cytokines, particularly IL-12, upon antigen encounter and can thus influence the ensuing adaptive immune response. As DC are phagocytic antigen-presenting cells located at sites exposed to bacterial invaders, studies have been performed to gain insight into the role of DC in combating bacterial infections. Indeed, studies with Salmonella have shown that DC can internalize and process this bacterium for peptide presentation on MHC-II as well as MHC-I. DC can also act as bystander antigen--presenting cells by presenting Salmonella antigens after internalizing neighbouring cells that have undergone Salmonella-induced apoptotic death. DC also produce IL-12 and TNF-alpha upon Salmonella encounter. Moreover, studies in a murine infection model have shown that splenic DC increase surface expression of co-stimulatory molecules during infection, and DC contain intracellular bacteria. In addition, quantitative changes occur in splenic DC numbers in the early stages of oral Salmonella infection, and this is accompanied by redistribution of the defined DC subsets in the spleen of infected mice. DC from Salmonella-infected mice also produce cytokines and can stimulate bacteria-specific T cells upon ex vivo co-culture. In addition, DC may play a role in the traversal of bacteria from the intestinal lumen. Studying the function of DC during Salmonella infection provides insight into the capacity of this sophisticated antigen-presenting cell to initiate and modulate the immune response to bacteria.
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Affiliation(s)
- Malin Sundquist
- Department of Clinical Immunology, Göteborg University, Göteborg, Sweden
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25
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Tournier JN, Hellmann AQ, Lesca G, Jouan A, Drouet E, Mathieu J. Fever-like thermal conditions regulate the activation of maturing dendritic cells. J Leukoc Biol 2003; 73:493-501. [PMID: 12660224 DOI: 10.1189/jlb.1002506] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Fever is one of the most frequent clinical signs encountered in pathology, especially with respect to infectious diseases. It is currently thought that the role of fever on immunity is limited to activation of innate immunity; however, its relevance to activation of adaptive immunity remains unclear. Dendritic cells (DCs) that behave as sentinels of the immune system provide an important bridge between innate and adaptive immunity. To highlight the role of fever on adaptive immunity, we exposed murine bone marrow-derived lipopolysaccharide (LPS)- or live bacteria-maturing DCs over a 3-h period to 37 degrees C or to fever-like thermal conditions (39 degrees C or 40 degrees C). At these three temperatures, we measured the kinetics of cytokine production and the ability of DCs to induce an allogeneic mixed lymphocyte reaction. Our results show that short exposure of DCs to temperatures of 39 degrees C or 40 degrees C differentially increased the secretion of interleukin (IL)-12p70 and decreased the secretion of IL-10 and tumor necrosis factor alpha by maturing DCs. These fever-like conditions induced a regulation of cytokine production at the single-cell level. In addition, short-term exposed LPS-maturing DCs to 39 degrees C induced a stronger reaction with allogeneic CD4(+) T cells than maturing DCs incubated at 37 degrees C. These results provide evidence that temperature regulates cytokine secretion and DC functions, both of which are of particular importance in bacterial diseases.
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Affiliation(s)
- Jean-Nicolas Tournier
- Département de Biologie des agents Transmissibles, Centre de Recherches du Service de Santé des Armées, La Tronche cedex, France.
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26
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Abstract
Dendritic cells (DC) are an important link between the innate and adaptive immune response and are key antigen presenting cells in triggering specific immunity. This review summarizes the role of DC and the DC subsets during infection with the facultative intracellular bacterium Salmonella. The capacity of DC to stimulate Salmonella-specific T cells by direct and indirect presentation of Salmonella antigens as well as the cytokine production capacity of DC upon Salmonella encounter are discussed. In addition, changes in the number, localization and cytokine production by splenic DC subsets during infection are reviewed. Studying the function of DC during Salmonella infection provides insight into the capacity of this phagocytic antigen presenting cell to initiate and modulate an immune response during bacterial infection.
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Affiliation(s)
- Mary Jo Wick
- Department of Clinical Immunology, University of Göteborg, Guldhedsgatan 10, SE-413 46, Göteborg, Sweden.
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27
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Arad-Yellin R, Firer M, Kahana N, Green BS. Functionalized polysulfone as a novel and useful carrier for immunization and antibody detection. REACT FUNCT POLYM 2003. [DOI: 10.1016/s1381-5148(02)00178-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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28
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Palucka K, Banchereau J. How dendritic cells and microbes interact to elicit or subvert protective immune responses. Curr Opin Immunol 2002; 14:420-31. [PMID: 12088675 DOI: 10.1016/s0952-7915(02)00365-5] [Citation(s) in RCA: 167] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
B and T lymphocytes recognize antigens with high specificity, but neither initiate immune responses, nor decide their types. These functions rest upon dendritic cells (DCs), which can determine and maintain Th1/Th2 polarization. Immune responses are thus dependent on the DC subset, the receptors that recognize each pathogen and the microenvironment. Microbes employ an array of mechanisms to evade and disrupt DC functions; some even hijack DCs for transport around the body. Our progress in the understanding of DC physiology will hopefully help us create the necessary vaccines to counteract the infectious agents that still plague mankind.
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Affiliation(s)
- Karolina Palucka
- Baylor Institute for Immunology Research, Dallas, TX 75204, USA.
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29
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Abstract
One type of phagocytic antigen-presenting cell (APC) - the dendritic cell (DC) - may have specialized functions during infection with the bacterium Salmonella, including a possible role in transporting Salmonella across the intestinal barrier. In addition, changes in the number, localization and cytokine production of CD8alpha+, CD8alpha-CD4+ and CD8alpha-CD4- DC subsets occur during infection. DCs function in stimulating bacteria-specific T cells by direct presentation of Salmonella antigens and as bystander APCs. Studying the function of DCs during Salmonella infection provides insight into the capacity of these sophisticated APCs, which are a key link between innate and adaptive immunity, to initiate and modulate the immune response to a bacterial infection.
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Affiliation(s)
- Mary Jo Wick
- Department of Clinical Immunology, University of Göteborg, Guldhedsgatan 10, Göteborg, Sweden.
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30
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Abstract
Successful immunity against Salmonella infections is dependent on the generation of CD4(+) T helper cells and to a lesser extent on antibody production and CD8(+) T cells. The cells within the lymphatic tissue of the gut are likely to be central for the orchestration of a proper and rapid response. The anatomical restriction of the pathogen may also determine the distribution of effector cells. In this issue of Immunity, McSorley et al. address both of these processes using identifiable CD4 T cells that are specific for Salmonella typhimurium. Such cells localize to the Peyer's patches of the small intestine when the bacteria are delivered orally.
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Affiliation(s)
- Eric A Hughes
- Section of Microbial Pathogenesis, Yale School of Medicine, New Haven, CT 06536, USA
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31
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Kaufmann SH, Raupach B, Finlay BB. Introduction: microbiology and immunology: lessons learned from Salmonella. Microbes Infect 2001; 3:1177-81. [PMID: 11755405 DOI: 10.1016/s1286-4579(01)01498-8] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Salmonella enterica, a Gram-negative bacterium, causes significant morbidity and mortality worldwide, and is an excellent model to study bacterial pathogenesis and cellular immune responses. With the development of powerful new technologies, there has been a fusion of research on immunology, molecular biology and cellular microbiology of S. enterica infections. This multidisciplinary research will enhance our understanding of the basic mechanisms of bacterial infections and immunity; it also provides new approaches towards therapeutic and control measures.
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Affiliation(s)
- S H Kaufmann
- Department of Immunology, Max Planck Institute for Infection Biology, Schumannstr. 21/22, 10117 Berlin, Germany.
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