Immunity Responds to Listeria monocytogenes


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These Slides are my presentation in M.s degree in Immunology lesson for my Classmates at my university. You can found important information about Virulence factors of Listeria monocytogenes that can Scape from immune responds and defeat them.

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  • Propulsion :فشار به سوی جلو، نیروی محرکه
  • Immunity Responds to Listeria monocytogenes

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    2. 2. Qazvin university of Medical Science, Fall 1392 2
    3. 3.       Listeria monocytogenes is a Gram-positive pathogenic bacterium that has adapted to various environments, from soils and food products to the intestinal tract and intracellular compartments of diverse animal species and humans. The aerobic Non–spore-forming Catalse Positive The organisms are motile at room temperature (25 ̊C) but less so at 37 °C L. monocytogenes exhibits weak β-hemolysis when grown on sheep blood agar plates. 3
    4. 4. L. monocytogenes is a facultative intracellular pathogen that can live both inside and outside its host.  To infect its mammalian host and to cause the most severe pathologies, L. monocytogenes is able to cross :  The intestinal  Blood-brain and  Maternofetal barriers  Crossing the host barriers involves bacterial invasion and survival within a large variety of normally nonphagocytic cells  It is therefore crucial to understand how L. monocytogenes induces its own uptake by host cells.  4
    5. 5. Listeriosis manifests itself through flu-like symptoms and can lead to  diarrhea,  meningitis,  encephalitis,  meningoencephalitis and  Stillbirths In humans, it primarily infects immunocompromised individuals like  pregnant women,  neonates, and  the elderly  5
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    7. 7. Listeriosis is a severe foodborne disease characterized by bacteremia and meningoencephalitis in individuals with impaired cell-mediated immunity, Including :  Neonates,  Pregnant woman,  Elderly persons, and  Immunosuppressed patients.  The potential of L. monocytogenes to cause disease correlates with its capacity to survive within macrophages, to invade nonphagocytic cells and replicate therein and also to cross the intestinal, the blood– brain, and the fetoplacental barriers.  7
    8. 8. The incidence of listeriosis is rather low, compared to other common foodborne pathogens such as Campylobacter species, Salmonella species, Shigella species, andVibrio species. However  The outcome is much more severe and often fatal.  In fact, it represents one of the most deadly bacterial infections due to its high mean mortality rate of 20%– 30%, despite early antibiotic treatment.  8
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    10. 10.  Internalins Proteins (ex : InL A, InL B ,....) PI-PLC PC-PLC  Listeriolysin O (LLO)  Phospholipases  Act A  The Virulence Genes (prfA, PlcA, hly, mpl,...) 10
    11. 11.    There exist two principle mechanisms by which L. monocytogenes can enter into the host through the intestinal mucosa. The first route is direct invasion of the enterocytes lining the absorptive epithelium of the microvilli, leading to infection of the intestinal cells This entry mechanism occurs only in humans and some susceptible animals. The second entry pathway is translocation across the M-cells of Peyer’s patches. 11
    12. 12.  Internalin (InlA), and InlB were the first surface proteins of L.monocytogenes identified to promote host cell invasion.  They have an amino-terminal leucine-rich repeat domain (LRR) formed by tandem repeats of 20-22 amino acids. The LRR regions are structurally and functionally important to theninternalization of LM.   LRRs provide versatile recognition units for proteinprotein interactions and protein activation in a variety of prokaryotic and eukaryotic proteins. 12
    13. 13.     L. monocytogenes genome encodes 22 additional proteins containing LRRs that form the internalin family. The amino-terminal LRRs are followed by a conserved inter-repeat domain (IR) The carboxy-terminal LPXTG motif, which mediates covalent binding to the cell wall peptidoglycan, is present in 19 members including the internalin prototype, InlA One member, InlB, is bound to the lipoteichoic acids on the bacterial cell wall by electrostatic interactions involving carboxy-terminal glycine/tryptophan-rich (GW) modules. 13
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    16. 16.  InlA, an 800-amino-acid protein, is responsible for bacterial entry into epithelial cells.  InlA specifically interacts with E-cadherin.  E-cadherin: a member of the cadherin superfamily of calcium-dependent cell adhesion molecules.  E-cadherin is involved in the formation of adherens junctions in polarized epithelial cells of different tissues. 16
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    18. 18.     The carboxyl terminal of E-cadherin directly interacts with the intracellular β-catenin. α-catenin, in turn, binds to β-catenin and interacts with actin This interaction leads to the formation of a fusion molecule consisting of the ectodomains of the Ecadherin and the actin binding site of the α-catenin which eventually leads to LM entry. Furthermore, myosin VIIA and its ligand vezatin together function as the molecular motor in the internalization of Listeria. When myosin VIIA binds vezatin, coupled with an actin polymerization process, it provides the tension necessary for bacterial internalization. 18
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    20. 20. InlB, a 630-amino-acid protein, promotes L. monocytogenes entry into a large variety of mammalian cells including :  Epithelial cells  Endothelial cells  Hepatocytes  Fibroblasts The hepatocyte growth factor receptor (Met/HGF-R) has been identified as the major ligand for InlB responsible for L. monocytogenes entry into non-phagocytic cells, and for cell scattering and membrane ruffling induced by soluble InlB 20
    21. 21.   Met belongs to the family of receptor tyrosine kinases (RTKs), one of the largest and most important families of transmembrane signaling receptors expressed by a large variety of cells. Met plays crucial roles in :  Organ morphogenesis,  Cell proliferation,  Cell migration and differentiation,  And also in cell growth and invasion during metastasis in cancer cells 21
    22. 22.  InlB functionally mimics HGF, the natural Met ligand, through the binding of its LRRs.  As in the case of the InlA/E-cadherin interaction, InlB interaction with Met is species specific: InlB interacts with human and mouse Met, but does not recognize the guinea-pig or rabbit receptor. 22
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    25. 25. Listeriolysin O (LLO), the major and first identified virulence factor of L. monocytogenes is a member of the cholesterol-dependent cytolysin (CDC) family of toxins.  These toxins are produced by numerous Gram-positive bacterial pathogens including :  Streptococcus pneumonia  Bacillus anthracis.  Among these pathogens only L. monocytogenes is known to infect nonphagocytic cells and LLO, secreted by L. monocytogenes, is required for bacterial escape from endocytic vacuoles.  25
    26. 26.   LLO binds to the host plasma membrane as a monomer and then forms oligomers composed of up to 50 subunits that inserts into the plasma membrane forming pores of about 200e 300 A° diameter. hly, one of the many genes activated during infection, leads to the production of Listeriolysin O (LLO).  Unlike the other CDCs, pore formation by LLO is more efficient at low pH facilitating the disruption of endocytic membranes following acidification of the vacuoles.  This is a crucial function for cellular invasion of both phagocytic and nonphagocytic cells. 26
    27. 27.         LM also uses phospholipases C to aid in the escape from the vacuole. Two specific phospholipases (PLCS) are used. One is the phosphatidylinostiol-specific PLC (PI-PLC), and The other is more general, phosphatidylinostiol-specific (PCPLC). The role of the PI-PLC secreted by LM is to catalyze the production of inositol phosphate and diacylglycerol (DAG) through cleavage of the membrane lipid PI. DAG then has the ability to activate protein kinase C (PKC). There are four types of PKCs, but the PKC of the host is shown to be linked with the PI-PLC signaling cascade. The PKC has been shown to facilitate the permeation of the phagosomal membrane before the bacteria escape. 27
    28. 28. In summary, the secretion of PLCs during listerial infection has several effects on the host cell. One of these effects has been shown to : 1) Increase the permeation of phagosomal membrane. 2) The activation of PKC through PI-PLC facilitates the escape of the bacterium. 3) The decreased affinity of L. monocytogenes for the glycan linker of the GPI-anchored protein due to the lack or absence of the Vb-strand also increases the ability for the bacterium to escape during infection. 4) PC-PLC leads to the activation of NF-kB, which allows the bacteria to exploit the host cell machinery.  28
    29. 29.    The bacterial surface protein ActA is a major virulence factor of L. monocytogenes that enables bacterial propulsion in the cytosol leading to the invasion of yet uninfected neighboring cells by a process called cell-tocell spreading. Host cell interaction could be mediated by the aminoterminal region of ActA that has several clusters of positively charged amino-acids that could bind heparan sulfate proteoglycans. The precise mechanism involved in ActA -mediated invasion remains to be elucidated. 29
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    36. 36.  After infection within the gastrointestinal tract immediate immune responses are essential for the control of pathogens, such as L. monocytogenes.  Activation of the innate immune system is triggered when pathogen-associated molecular patterns (PAMPs) engage pattern recognition receptors (PRRs) on intestinal epithelial cells (IECs). 36
    37. 37.  Typical PAMPs include bacterial carbohydrates, such as  Lipopolysaccharide (LPS) Mannose Nucleic acids (both DNA and RNA) Peptidoglycan components Lipoteichoic acids, and probably many other molecules, and are able to trigger the innate immune response.     37
    38. 38.     Innate immunity to L. monocytogenes is primarily mediated by two types of pattern recognition receptors: The Toll-like receptors (TLRs) The nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs). In addition, there is some experimental evidence for the involvement of scavenger receptors and a TLR-9 independent cytosolic sensor system for bacterial DNA 38
    39. 39. Upon recognition of the presence of microbes through sensing pathogen-associated molecular patterns.  TLRs can bind any of the 4 known activating adaptors:  Myeloid differentiating factor-88 (MyD88)  MyD88 adapter-like (Mal)  TIR domain-containing adapterinducing IFN-ɣ (TRIF)  TRIF-related adapter molecule (TRAM)  39
    40. 40.  MyD88 appears to be the key adaptor molecule, because it is required for signaling by all TLRs with only one exception: TLR3 uses TRIF.  The binding of the activating adaptors results in the subsequent recruitment of IL-1R, associated kinases (IRAKs) and downstream activation of transcription factors including NF-κB and IFN regulatory factor 3 (IRF3), which in turn induces the proinflammatory cytokines and type I IFNs. 40
    41. 41. Toll-like receptor 2 (TLR2) can interact with several specific ligands, including :  Bacterial lipoproteins  Lipoteichoic  Acids of Gram-positive bacteria such as L. monocytogenes  Yeast zymosan   TLR2 can form heterodimers with TLR1 and TLR6, thereby improving the recognition of the target lipoteichoic acids. 41
    42. 42.  TLR2 is expressed on the cell surface of intestinal epithelial cells and its activation by commensal bacteria is thought to play an important role in the maintenance of the integrity of the intestinal epithelial barrier.  TLR2 is also expressed within phagolysosomes, thus, L. monocytogenes cells that have escaped into the host cell cytoplasm were not detected by TLR2.  The importance of TLR2 signaling for early protection against L. monocytogenes is, however, inconclusive. 42
    43. 43.  Toll-like receptor 5 (TLR5) can bind to a protein motif common to the flagellin protein making up the flagella from many bacteria, such as L. monocytogenes.  TLR5 activation induces NF-κB and stimulates TNF production, suggesting that TLR5 may serve as a general alarm system, when the gastrointestinal barrier is compromised by a broad spectrum of motile bacteria. 43
    44. 44.  Toll-like receptor 9 (TLR9) recognizes the CpG motifs present in bacterial DNA. In immune cells, TLR9 is exclusively localized in the endosomes.  In the intestine, TLR9 was shown to be located on both, the apical and the basolateral surface of IECs.  Upon activation of TLR9, IκBα is degraded and NF-κB is activated, again resulting in a proinflammatory response. 44
    45. 45.  In conclusion, the available experimental evidence suggests that TLR2 is the most relevant TLR for recognition of L. monocytogenes cells However, as IECs show.  TLR2 commensal ligand-induced activation, TLR2 is also considered to play an important role in maintaining the integrity of the intestinal epithelial barrier. 45
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    49. 49.  The NLRs are critical for mucosal innate immunity as sensors of microbial components and cell injury in the cytoplasm.  Both NOD1 and NOD2 are important for the innate immune response against L. monocytogenes, because they represent intracellular sensors of bacterial peptidoglycan components that are thought to enter cells by endocytosis through clathrin-coated pits. 49
    50. 50.   NOD1 is ubiquitously expressed in adult human Tissues. NOD2 is expressed only in leukocytes, DCs, and epithelial cells. Activation of NOD1 and NOD2 results in the translocation of NF-κB and mitogen-activated protein kinase into the nucleus, to up-regulate the transcription of proinflammatory genes and mediate antibacterial effects by the up-regulation of another group of small antibacterial peptides, the defensins.  50
    51. 51.  NOD1 recognizes a diaminopimelic acid-containing dipeptide or tripeptide molecule generated by lysozyme action on the peptidoglycan of many Gram-negative and Gram-positive bacteria, including L. monocytogenes.  NOD2 is activated by muramyl dipeptide (MDP), which is another degradation product of the peptidoglycan produced by lysozyme and other (bacterial) peptidoglycan hydrolases. 51
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    53. 53.  DCs respond to different pathogens and initiate the appropriate type of T cell response needed to control the infection.  In response to L. monocytogenes infection, DCs are critical in priming the T cell response, since mice depleted of DCs are unable to generate a CD8 T cell response.  Due to the primarily intracellular localization of L. monocytogenes, CD4 and CD8 T cells mediate most of the adaptive immune response, and are crucial for longtermimmunity after initial L. monocytogenes infection. 53
    54. 54.   Almost any cell type that harbors L. monocytogenes in the cytoplasm can process the proteins secreted from the pathogen, by degradation and subsequent loading on MHC class I molecules, in order to present them on the cell surface to CD8 T cells. Only professional antigen presenting cells (APCs) can present antigens derived from lysosomal degradation via the MHC class II pathway to CD4 T cells. 54
    55. 55. The CD8 T cells mediate the anti-Listeria immunity by two synergistic mechanisms: first:  by secretion of IFN-γ to activate macrophages; Secondly: by lysis of infected cells via perforin and granzymes, leading to the exposure of intracellular bacteria to the activated macrophages  55
    56. 56.  IFN-γ is known to be essential for host resistance to intracellular pathogens such as L. monocytogenes, as it mediates the activation of resting macrophages that more efficiently restricts the multiplication of intracellular pathogens and promotes long-term protective cellular immunity. 56
    57. 57.  L. monocytogenes induces a strong T-helper type 1 response and, similar to CD8 T cells, CD4 T cells also secrete IFN-γ.  The strong CD8 and CD4 T cell responses results in a stable population of memory T cells specific for L. monocytogenes 57
    58. 58.  In the intestine, NKT cells (lymphocytes expressing both NK and T cell markers) play an important role in the control of early infection with L. monocytogenes.  In general, adaptive immune responses in the intestine are characterized by high numbers of IgA producing plasma cells, regulatory T cells, and IL-17 producing T cells whose development is closely linked to factors produced by PRRs expressing IECs, DCs, and macrophages. 58
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