12.1 Immunity to Viruses and Parasites
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Questions and Answers

What is one of the main consequences of sepsis caused by severe infections?

  • Increased local inflammation only
  • Inhibition of protein synthesis
  • Systemic disorders of tissue perfusion (correct)
  • Complete immune system shutdown

    • Which cytokines are primarily involved in mediating sepsis?

  • IL-1, TGF-beta, and IL-12
  • IL-8, IL-10, and interferon-gamma
  • IL-2, IL-4, and TNF-alpha
  • IL-6, IL-1, and TNF (correct)

    • How do bacteria with polysaccharide-rich capsules evade phagocytosis?

  • By blocking antibody binding sites
  • By replicating rapidly within host cells
  • By inhibiting the fusion of phagosomes and lysosomes (correct)
  • By forming biofilms in the bloodstream

    • Which mechanism helps bacteria evade humoral immunity?

    <p>Variation of surface antigens</p> Signup and view all the answers

    What potential outcome can result from the production of antibodies against bacterial cell wall antigens after a streptococcal infection?

    <p>Myocarditis</p> Signup and view all the answers

    What type of immunity primarily protects against extracellular bacteria?

    <p>Humoral immunity</p> Signup and view all the answers

    Which cytokine is associated with the attraction of neutrophils by innate lymphoid cells (ILCs)?

    <p>IL-17</p> Signup and view all the answers

    Which of the following is NOT a role of CD4+ helper T cells in the immune response to extracellular bacteria?

    <p>Directly killing infected cells</p> Signup and view all the answers

    What is a potential injurious effect of the immune response to extracellular bacteria?

    <p>Tissue damage from inflammation</p> Signup and view all the answers

    Which antibody isotype is primarily responsible for neutralizing toxins from extracellular bacteria?

    <p>IgG3</p> Signup and view all the answers

    What is a primary event that occurs during the development of an infectious disease?

    <p>Entry of the microbe</p> Signup and view all the answers

    Which of the following represents a method by which microbes produce disease?

    <p>Direct killing of host cells</p> Signup and view all the answers

    What role do toxins play in microbial disease?

    <p>They cause tissue damage and functional issues</p> Signup and view all the answers

    What is meant by 'immune evasion' in the context of pathogens?

    <p>Resisting or avoiding immune responses</p> Signup and view all the answers

    Which mechanism is primarily involved in the phagocytosis of extracellular bacteria?

    <p>Complement receptor engagement</p> Signup and view all the answers

    What type of immunity is activated by the presence of extracellular bacteria?

    <p>Both innate and adaptive immunity</p> Signup and view all the answers

    Inherited and acquired defects in which type of immunity can lead to increased susceptibility to infections?

    <p>Innate and adaptive immunity</p> Signup and view all the answers

    How do microbes establish persistent infections in a host?

    <p>By controlling the immune response without elimination</p> Signup and view all the answers

    What is the role of IFN-γ in protozoal infections?

    <p>It protects against many protozoal infections.</p> Signup and view all the answers

    Which of the following mechanisms primarily mediates defense against helminthic infections?

    <p>Activation of Th2 cells and IgE production.</p> Signup and view all the answers

    What happens when IgE binds to eosinophils and mast cells?

    <p>It activates eosinophils to release their granule contents.</p> Signup and view all the answers

    What is a characteristic of stage-specific antigenic variation in malaria parasites?

    <p>It causes sporozoites to express different antigens than merozoites.</p> Signup and view all the answers

    What best describes the continuous variation of major surface antigens in parasites?

    <p>It ensures parasites can stay hidden from a static immune system.</p> Signup and view all the answers

    What is one primary mechanism that influenza viruses use for antigenic variation?

    <p>Reassortment</p> Signup and view all the answers

    Which of the following is NOT a method by which some viruses inhibit immune responses?

    <p>Activating Th1 cells</p> Signup and view all the answers

    Which immune cells are primarily involved in responding to helminth infections?

    <p>Eosinophils</p> Signup and view all the answers

    What is a significant reason for the chronic nature of many parasitic infections?

    <p>Weak innate immunity</p> Signup and view all the answers

    Which step do some viruses block to inhibit MHC class I presentation?

    <p>Transport of proteins</p> Signup and view all the answers

    Which immune mechanism is critical for targeting protozoa that survive inside macrophages?

    <p>Cell-mediated immunity</p> Signup and view all the answers

    What role do TLR2 and TLR4 play in the immune response to protozoa?

    <p>Initiate phagocytosis</p> Signup and view all the answers

    What outcome is associated with chronic viral infections regarding CTL responses?

    <p>Exhaustion of CTL responses</p> Signup and view all the answers

    What is the primary mechanism by which intracellular bacteria evade elimination by the immune system?

    <p>Resistance to phagocyte-mediated elimination</p> Signup and view all the answers

    Which cells are predominantly involved in the innate immune response to intracellular bacteria?

    <p>Phagocytes and NK cells</p> Signup and view all the answers

    What role do CD4+ T cells play in the adaptive immune response to intracellular bacteria?

    <p>Activate phagocytes to kill microbes</p> Signup and view all the answers

    Which of the following is NOT a primary mediator of innate immunity against fungi?

    <p>IL-12</p> Signup and view all the answers

    What mechanism primarily allows cytotoxic T lymphocytes (CTLs) to eliminate virus-infected cells?

    <p>Recognition of virus antigens presented by MHC I</p> Signup and view all the answers

    How do type I interferons function in the context of viral infections?

    <p>Inhibiting viral replication in infected cells</p> Signup and view all the answers

    Which type of immune response is primarily effective against extracellular fungal infections?

    <p>Th17 response</p> Signup and view all the answers

    What cytokines are produced by phagocytes which are essential for the activation of NK cells during the immune response to intracellular bacteria?

    <p>IL-12 and IL-15</p> Signup and view all the answers

    Which immune mechanism primarily functions during the extracellular stage of a viral infection?

    <p>Antibody-mediated neutralization</p> Signup and view all the answers

    Which of the following statements about immune evasion by intracellular bacteria is true?

    <p>They often lead to chronic infections difficult to eliminate.</p> Signup and view all the answers

    Which cells are primarily responsible for the secretion of cytokines that induce leukocyte infiltration during the inflammatory response?

    <p>Phagocytes and dendritic cells</p> Signup and view all the answers

    Which antibody isotype is most effective in blocking infections and neutralizing toxins from extracellular bacteria?

    <p>IgG</p> Signup and view all the answers

    What is a key function of CD4+ helper T cells in the immune response to extracellular bacteria?

    <p>Stimulate antibody production</p> Signup and view all the answers

    Which of the following best describes a consequence of inflammation caused by the immune response to extracellular bacteria?

    <p>Tissue damage from local production of reactive oxygen species</p> Signup and view all the answers

    Which cytokines can innate lymphoid cells (ILCs) secrete to attract neutrophils during an immune response?

    <p>IL-17 and IL-22</p> Signup and view all the answers

    What is a common pathological consequence of severe infections caused by certain bacteria?

    <p>Sepsis</p> Signup and view all the answers

    Which of the following antibodies can cross-react with myocardial proteins leading to myocarditis?

    <p>IgG against bacterial cell wall antigens</p> Signup and view all the answers

    How do pathogenic bacteria use surface structures to evade immune responses?

    <p>By varying their surface antigens</p> Signup and view all the answers

    What is one potential outcome of the immune evasion tactics employed by extracellular bacteria?

    <p>Persistent bacterial infections</p> Signup and view all the answers

    What role do bacterial superantigens, such as staphylococcal enterotoxin B, play in immune responses?

    <p>They cause polyclonal activation of T cells</p> Signup and view all the answers

    Which factor primarily contributes to the progression of infections after a pathogen enters the host?

    <p>Evasion of host immunity</p> Signup and view all the answers

    What is the primary means by which extracellular bacteria induce inflammation in host tissues?

    <p>Toxin release causing tissue damage</p> Signup and view all the answers

    Which mechanism of innate immunity helps recognize extracellular bacteria by using specific receptors?

    <p>Phagocytosis by neutrophils</p> Signup and view all the answers

    Which of the following statements best describes one role of the complement system in response to Gram-positive bacteria?

    <p>Activates the alternative pathway through peptidoglycans</p> Signup and view all the answers

    How do some pathogens establish persistent infections within a host?

    <p>By evading or resisting immune effector mechanisms</p> Signup and view all the answers

    Which of the following is an injurious effect of the immune response to extracellular bacteria?

    <p>Destruction of normal tissues</p> Signup and view all the answers

    What type of bacteria are characterized by their ability to replicate outside of host cells?

    <p>Extracellular bacteria</p> Signup and view all the answers

    Which component of the immune system primarily mediates responses to extracellular pathogens such as bacteria?

    <p>B cells and antibodies</p> Signup and view all the answers

    What is the primary mechanism of antigenic variation employed by influenza viruses?

    <p>Reassortment of genetic material</p> Signup and view all the answers

    How do some viruses inhibit class I MHC presentation?

    <p>By inhibiting antigen processing and transport</p> Signup and view all the answers

    Which characteristic is associated with chronic viral infections?

    <p>Exhaustion of cytotoxic T lymphocytes (CTLs)</p> Signup and view all the answers

    What is the primary innate immune response to protozoa?

    <p>Phagocytosis</p> Signup and view all the answers

    What cell type primarily responds to helminth infections?

    <p>Eosinophils</p> Signup and view all the answers

    What role do Th1 cell-derived cytokines play in defending against protozoa?

    <p>Activating macrophages for enhanced killing</p> Signup and view all the answers

    Which of the following factors contributes to the chronic nature of parasitic infections?

    <p>Resistance of parasites to immune responses</p> Signup and view all the answers

    What is one way that viruses can inhibit the immune response?

    <p>By encoding soluble cytokine receptors</p> Signup and view all the answers

    What is the role of IL-4 in the immune response to helminthic infections?

    <p>Stimulates production of IgE antibodies</p> Signup and view all the answers

    Which cells are primarily activated in response to IgE coating helminths?

    <p>Eosinophils</p> Signup and view all the answers

    What type of antigenic variation occurs in malaria parasites between their infective sporozoite stage and the merozoite stage?

    <p>Stage-specific change in antigen expression</p> Signup and view all the answers

    How does the cytokine IFN-γ contribute to the immune response against protozoal infections?

    <p>Enhances macrophage activation</p> Signup and view all the answers

    What is the significance of IL-5 in the defense against helminthic infections?

    <p>Activates eosinophils</p> Signup and view all the answers

    Which immune cells are primarily responsible for recognizing intracellular bacteria?

    <p>Macrophages and NK cells</p> Signup and view all the answers

    What is the main immune mechanism used by CD4+ T cells to combat intracellular bacteria?

    <p>Activating phagocytes via CD40 ligand and IFN-γ</p> Signup and view all the answers

    Which cytokines are produced by phagocytes to activate natural killer (NK) cells during the immune response to intracellular bacteria?

    <p>IL-12 and IL-15</p> Signup and view all the answers

    How do type I interferons inhibit viral replication?

    <p>By inhibiting viral RNA translation in infected cells</p> Signup and view all the answers

    What is the role of CD8+ cytotoxic T lymphocytes (CTLs) in the immune response to viral infections?

    <p>Eliminating virus-infected cells</p> Signup and view all the answers

    What characterizes the immune response to fungal infections?

    <p>Significant involvement of neutrophils and macrophages</p> Signup and view all the answers

    Why do intracellular bacteria often cause chronic infections?

    <p>By resisting phagocyte-mediated elimination</p> Signup and view all the answers

    What role do antibodies play in the immune response to viral infections?

    <p>They neutralize viruses and inhibit their entry into cells</p> Signup and view all the answers

    Which of the following is true regarding the immune response to intracellular fungi?

    <p>The response mainly involves cell-mediated immunity</p> Signup and view all the answers

    Study Notes

    Immunity to Pathogens

    • Immunity to pathogens is mediated by innate and adaptive immunity effector mechanisms
    • The immune system responds in specialized ways to different types of microbes
    • Microbes' survival and pathogenicity depend on their ability to evade or resist the host's immunity
    • Microbes can establish latent infections where the immune system controls but doesn't eliminate the pathogen
    • Inherited and learned immune defects influence susceptibility to infections

    Development of Infectious Disease

    • Key events during infection include pathogen entry, invasion, colonization of host tissues, evasion of host immunity, and tissue injury/functional impairment

    Microbe-Induced Disease

    • Microbes cause disease by directly killing host cells
    • Release toxins that damage tissue
    • Stimulate immune responses, harming normal tissue

    Progression and Outcome of Infections

    • Infections progress from an incubation period, through disease, to either complete eradication by the host or to chronic, recurrent disease or death, depending on innate and adaptive responses. The outcome can vary based on the type of pathogen and the host's immune response.

    Overview of Immune Responses to Pathogens

    • Effector mechanisms of innate and adaptive immunity mediate immunity against microbes
    • The immune system responds differently based on microbe type
    • Microbe survival and pathogenicity are linked to their ability to evade or resist immune mechanisms

    Immunity to Extracellular Bacteria

    • Extracellular bacteria replicate outside host cells (e.g., blood, connective tissue, respiratory/GI tracts)
    • They cause inflammation and release toxins, causing tissue injury
    • Innate immunity to extracellular bacteria involves complement activation (alternative and lectin pathways), phagocytosis (using e.g., mannose/scavenger, Fc, complement receptors), and the inflammatory response (using cytokines from phagocytes and innate lymphoid cells like IL-17, IL-22)
    • Adaptive immunity involves a humoral response with antibodies that neutralize toxins and opsonize bacteria for phagocytosis via Fc-receptors
    • Helper T cells stimulate antibody production, enhance phagocytic activity of macrophages and neutrophils.
    • Injurious effects include inflammation, often characterized by ROS/lysosomal enzyme release and ultimately self-limiting, and sepsis, a systemic effect of severe infection (G+/G-bacteria). Sepsis includes disruptions in tissue perfusion, coagulation, metabolism and organ failure, potentially leading to septic shock.

    Immunity to Intracellular Bacteria

    • Intracellular bacteria live and replicate within host cells, making them inaccessible to circulating antibodies
    • Their elimination requires cell-mediated immunity
    • Innate immunity involves phagocytes and natural killer cells (recognizing bacteria with TLRs and NOD-like receptors, activating NK cells with IL-12/IL-15), which disrupt bacterial replication
    • Adaptive immunity relies on CD4+ T cells activating phagocytes, and CD8+ T cells killing infected cells.
    • Inappropriately activated macrophages and the damage that follows can cause tissue injury

    Immune Evasion by Intracellular Bacteria

    • Bacteria can avoid phagocytic mechanisms, like inhibiting phagolysosome formation or disrupting phagosome function, and escape into the cytoplasm. Some bacteria can avoid reactive oxygen species/nitrogen species.

    Immunity to Fungi

    • Fungal infections, or mycoses, are opportunistic diseases in immunocompromised hosts
    • Some fungi reside within and/or between host cells, such as within phagocytes
    • Innate immunity involves neutrophils, macrophages, and ILCs; detecting them through TLRs and Dectins. These use cytokines to recruit neutrophils, stimulating phagocytosis via ROS and lysosomal enzymes
    • Adaptive immunity involves cell-mediated immunity (CD4+/CD8+ T cells) for intracellular fungal killing

    Immunity to Viruses

    • Viruses are obligatory intracellular pathogens
    • Replication interferes with normal cellular function leading to cytopathic effects
    • Innate immunity involves antiviral states, type I interferons that inhibit replication in infected/uninfected cells and NK cell-mediated killing of infected cells
    • Adaptive immunity involves neutralizing antibodies when the virus is extracellular and CTLs (CD8+ T cells) to kill infected cells

    Immune Evasion by Viruses

    • Viruses evade the immune response through antigenic shift/variation, inhibition of MHC molecules' function (e.g., blocking MHC molecule presentation, preventing antigen processing/transport/presentation, producing NK cell inhibitory receptors, inhibiting access of the innate immunity sensor systems, interfering with signaling of the innate sensor systems like PKR/signaling by IFN receptors).
    • Viruses generate soluble cytokine receptors and inhibit CTL responses (e.g., exhaustion of CTLs through sustained antigen stimulation/PD-1 receptor expression).
    • Viruses may directly target immune cells such as CD4+T cells.

    Immunity to Parasites

    • Parasites include protozoa, helminths, and ectoparasites
    • Many parasitic infections are chronic due to limited innate immunity, evasion/resistance to adaptive immune responses, and limited antiparasitic drugs
    • Innate immunity to protozoa depends primarily on phagocytosis by phagocytes, with recognition by TLR2/TLR4
    • Eosinophils play a large role in response to helminths
    • Adaptive immunity to parasites demonstrates distinct responses depending on parasite type

    Challenges of Parasitic Antigens

    • Antigens vary in their expression levels and type at different stages of the parasite's life cycle
    • Antigenic variation (stage or continuous) are a significant challenge for the host immune system to combat infections appropriately.

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    Immunity to Viruses and Parasites PDF

    Description

    This quiz covers essential concepts from Microbiology Chapter 5, focusing on the immune response to extracellular bacteria and the consequences of sepsis. Test your knowledge on cytokines, immune mechanisms, and the role of antibodies in combating bacterial infections.

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