TLR4 protein are susceptible to infections from Gram-negative bacteria. Why are these patients vulnerable to this particular type of pathogen?
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TLR4 protein are susceptible to infections from Gram-negative bacteria. Why are these patients vulnerable to this particular type of pathogen?
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- Patients with recurrent infections of Neisseria meningitidis, an extracellular bacterial pathogen that causes meningitis, were examined to determine the underlying cause of their immunodeficiency. A subset of these patients were found to have defects in complement activation on the bacterial surface, a process that for this bacterium is dominated by alternative complement activation leading to C3b deposition on the pathogen surface. When neutrophils from these patients were examined in vitro, the results, in the figure below, were obtained. Based on these data, the identity of the green neutrophil mediator in the figure below is likely to be: Complement factor B The C3 convertase Factor P (properdin) C3b Mannose-binding lectin (MBL)Explain the mechanism underlying the molecular structure of C7, C8, and C9 complement protein that facilitates their insertion into the cell membrane of a pathogen?The terminal complement proteins polymerize to form pores in membranes that can kill certain pathogens. The terminal components of the complement pathway assemble to form a membrane attack complex that can induce pathogen lysis and death. Yet, evidence indicates that this feature of complement is less important than the earlier steps that promote pathogen opsonization and induce inflammation. This conclusion is based on: In vitro experiments showing that very few species of bacteria are susceptible to lysis by the membrane attack complex Experiments indicating that only bacteria, but not viruses or fungi, are susceptible to lysis by the membrane attack complex The very low levels of terminal complement components in the serum The fact that other mammalian species lack the terminal components of the complement pathway needed to form the membrane attack complex The limited susceptibility to infections of patients with deficiencies in terminal complement components
- Some pathogenic microorganisms encode proteins, such as the Staphylococcus Protein A, that bind to immunoglobulin constant region domains with high affinity. These microbial proteins provide a benefit to the microorganism by: Preventing antibodies bound to the microbe from binding to Fc receptors on phagocytes Blocking the binding of anti-microbial antibodies to the pathogen surface Cleaving the antibody into fragments that separate the antigen-binding region from the effector function Inducing aggregation of the anti-microbial antibodies by multivalent binding to the pathogen-derived protein Preventing the antibody from neutralizing the pathogenThe current view in the field of immunology is that dendritic cells are the primary antigen-presenting cells for stimulating naive T cells. One piece of evidence supporting this conclusion is the observation that IRF8-deficient individuals, which retain their tissue-resident macrophages, are susceptible to a range of severe opportunistic infections caused by intracellular bacteria, viruses, and fungi. Explain the reasoning behind this argument.Would you predict that TLR-XX is able to recognize other types of Gram-negative bacteria, in addition to the one that was used in this experiment? Explain WHY or WHY NOT?see attached diagram.
- Antibody binding to a pathogen surface is greatly enhanced when both antigen-binding sites of the antibody are engaged at once, a feature known as bivalent binding. It is possible for antibodies to bind bivalently to a wide variety of components on many different pathogen surfaces due to the flexibility in the protein at the hinge region and at the V–C junction.Mannose binding lectins (MBL) and ficolins are the two classes of proteins that can initiate the lectin pathway of complement activation. These proteins are selective for activating complement on the surfaces of microbial pathogens rather than host cells because: Their higher-order oligomeric structure can be assembled only after the monomers first bind to pathogen membranes. They only recruit MASP (MBL-associated serine proteases) proteins when bound to pathogen surfaces and not when bound to host cells. They only undergo the conformational change needed to activate MASP proteins when bound to a pathogen and not when bound to a host cell. They only bind to carbohydrate side chains and oligosaccharide modifications found on pathogen surfaces but not on host cell membranes. The activated MASP proteins are rapidly inactivated by hydrolysis when present on the surface of a host cell.Mammalian Toll-like receptors are activated by many different pathogen-associated molecular patterns. As a family, TLRs can recognize PAMPs associated with a broad array of different pathogens, including bacteria, viruses, and fungi. Patients with a specific susceptibility to herpesvirus infections have a defect in their ability to respond to viral nucleic acids using TLR-3, TLR-7, or TLR-9, even though these proteins are expressed in the patients’ cells. Analysis of the TLRs in macrophages and dendritic cells from these patients would likely show which of the arrangements in Figure below?
- Mycobacteria are intracellular pathogens that have adapted to life inside phagocytic cells, such as macrophages. These intracellular bacteria are taken up by phagocytosis, similar to other pathogens, but the bacteria are not killed. One possible mechanism that could account for this immune evasion by mycobacteria is their ability to: Prevent induction of nitric oxide production in the phagosome Prevent the acidification of phagosomes Prevent the expression of antimicrobial peptides in the phagosome Prevent fusion of phagosomes with lysosomes Kill the macrophage before it kills themTLR-4 recognizes bacterial lipopolysaccharide in association with the host accessory proteins MD-2 and CD14. Stimulation of the nucleic acid sensing TLRs that reside in endosomal membranes induces the production of a different cytokine response than is produced by stimulation of the plasma membrane TLRs. In part, this distinction is based on the different adapter proteins used by the nucleic acid sensing TLRs, leading to the activation of IRF factors. The cytokine response following stimulation of nucleic acid-sensing TLRs is characterized by production of: The antiviral cytokine, type I interferon TNF-a, which induces increased vascular permeability Antimicrobial peptides by macrophages Chemokines that recruit neutrophils The inflammatory complement fragments, C3a and C5aThe classical complement pathway is initiated by C1q binding to the surface of a pathogen. In some cases, C1q can directly bind the pathogen, for instance by recognizing proteins of bacterial cell walls, but in most cases C1q binds to IgM antibodies that are bound to the pathogen surface. How does this IgM-binding feature of C1q contribute to rapid, innate immune responses rather than to slow, adaptive responses? C1q induces B lymphocytes to begin secreting antibody within hours of pathogen exposure. Natural antibody that binds to many microbial pathogens is produced prior to pathogen exposure. C1q binds to C-reactive protein which then binds to IgM on the pathogen surface. C1q directly induces inflammation, recruiting phagocytes and antibodies from the blood into the infected tissue. C1q binds to dendritic cells in the infected tissue, inducing them to secrete inflammatory cytokines.