lecture 29- immunity to infection
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Questions and Answers

What is the primary consequence of successful pathogen replication in the host?

  • It results in detectable clinical damage and disease. (correct)
  • It causes only immunopathic damage.
  • It leads to the immune system's instant failure.
  • It enables opportunistic pathogens to invade.

    • Which cells are responsible for mediating general innate defense at a cellular level?

  • B cells and plasma cells
  • Neutrophils and macrophages (correct)
  • M cells and T cells
  • Cytotoxic T cells and helper T cells

    • What characterizes the initial host defenses against pathogens?

  • M cells providing a direct route for pathogens.
  • The presence of antibodies in the bloodstream.
  • Intact skin and mucosal barriers. (correct)
  • The action of adaptive immune responses.

    • What role do acute phase proteins and pro-inflammatory cytokines play in response to a pathogen?

    <p>They trigger an inflammatory response to combat the pathogen.</p> Signup and view all the answers

    How do invasive pathogens typically gain access to the body?

    <p>By penetrating mucosal barriers or binding to host cell surface molecules.</p> Signup and view all the answers

    Which of the following receptors is NOT classified as a pattern recognition receptor (PRR)?

    <p>Complement receptors</p> Signup and view all the answers

    What role do soluble collectins play in the immune response?

    <p>They activate complement or stimulate phagocytosis.</p> Signup and view all the answers

    What is the primary function of neutrophils during an infection?

    <p>Eliminating pathogens via endocytosis and phagocytosis</p> Signup and view all the answers

    Which cells are primarily responsible for initiating the adaptive immune response after pathogen exposure?

    <p>Dendritic cells (DCs)</p> Signup and view all the answers

    What mechanism do extracellular bacteria often use to gain access to tissues?

    <p>Cleaving mucosal epithelium components</p> Signup and view all the answers

    What distinguishes exotoxins from endotoxins?

    <p>Exotoxins are secreted, while endotoxins are embedded in cell walls.</p> Signup and view all the answers

    In which areas do extracellular bacteria accumulate during infections?

    <p>Interstitial regions and the blood</p> Signup and view all the answers

    What immune response occurs when mature dendritic cells migrate to the lymph nodes?

    <p>Systemic immune response is generated.</p> Signup and view all the answers

    What is a common characteristic of both exotoxins and endotoxins regarding a Gram-negative bacterial species?

    <p>A species may produce both types of toxins.</p> Signup and view all the answers

    What triggers the influx of acute phase proteins and pro-inflammatory cytokines at the site of infection?

    <p>The penetration of skin or mucosae by a pathogen</p> Signup and view all the answers

    Which of the following best describes the biological interaction between pathogens and the immune system?

    <p>There is a constant battle between pathogen replication and immune elimination</p> Signup and view all the answers

    What is a possible consequence of immunopathic damage during an infection?

    <p>Unintentional injury to host tissues</p> Signup and view all the answers

    Which statement is true regarding the role of innate defense mechanisms?

    <p>They are the first line of defense and combat any type of pathogen</p> Signup and view all the answers

    How do opportunistic pathogens typically cause disease in hosts?

    <p>They exploit weaknesses when the immune system is compromised</p> Signup and view all the answers

    What is the role of leukocytes activated by pattern recognition receptor (PRR) engagement?

    <p>To eliminate pathogens or infected cells</p> Signup and view all the answers

    Which of the following cells primarily confront pathogens that reach the liver or spleen?

    <p>Resident macrophages</p> Signup and view all the answers

    What disease mechanisms do extracellular bacteria often employ to invade tissues?

    <p>Penetrating mucosal epithelium and utilizing surface receptors</p> Signup and view all the answers

    What triggers the activation of naïve T cells during an immune response?

    <p>Antigen recognition through pMHC presentation</p> Signup and view all the answers

    Which immune response is generated when mature dendritic cells migrate to the draining lymph node?

    <p>Systemic adaptive immune response</p> Signup and view all the answers

    What is a common source of symptoms caused by extracellular bacteria?

    <p>Toxin production by the bacteria</p> Signup and view all the answers

    What type of receptors are TLRs, NLRs, and RLRs classified as?

    <p>Pattern recognition receptors (PRRs)</p> Signup and view all the answers

    What role do chemokines play during an inflammatory response?

    <p>To draw leukocytes into the area of infection</p> Signup and view all the answers

    What are scavenger receptors primarily involved in?

    <p>Engaging in the recognition and elimination of pathogens</p> Signup and view all the answers

    Which statement accurately describes the relationship between pathogens and the immune system during an infection?

    <p>There is a continuous competitive interaction where both sides attempt to outmaneuver each other.</p> Signup and view all the answers

    What mechanism may allow invasive pathogens to bypass surface defenses?

    <p>Binding to host cell surface molecules that trigger internalization.</p> Signup and view all the answers

    Which type of pathogen is most likely to cause disease due to toxins regardless of colonization?

    <p>Extracellular bacteria, which can release toxins that affect host tissues.</p> Signup and view all the answers

    What factors determine the appropriate immune response to a particular pathogen?

    <p>The lifestyle and replication mode of the invading pathogen.</p> Signup and view all the answers

    What initiates the removal of pathogens by the complement system during an immune response?

    <p>The coating of pathogens by complement proteins like C3b.</p> Signup and view all the answers

    What is a significant mechanism through which leukocytes eliminate pathogens after PRR engagement?

    <p>Endocytosis or phagocytosis</p> Signup and view all the answers

    How do soluble collectins contribute to the immune response?

    <p>By binding to pathogens and activating complement</p> Signup and view all the answers

    In the context of extracellular bacteria, what role do exotoxins play?

    <p>They interfere with tissue structure and function</p> Signup and view all the answers

    Which statement is true regarding the transition to adaptive immunity?

    <p>Dendritic cells present pMHCs to naïve T cells to trigger activation</p> Signup and view all the answers

    What distinguishes endotoxins from exotoxins in terms of their release?

    <p>Endotoxins are released when Gram-negative cell walls are damaged</p> Signup and view all the answers

    What type of immune response is primarily generated by mature dendritic cells in the lymph nodes?

    <p>A systemic adaptive immune response</p> Signup and view all the answers

    Which cell type is crucial for innate defense against pathogens that reach the liver and spleen?

    <p>Resident macrophages</p> Signup and view all the answers

    What is a common outcome of the inflammatory response facilitated by chemokines?

    <p>Attraction of macrophages to the site of infection</p> Signup and view all the answers

    Which type of receptor is involved in the recognition of pathogen-associated molecular patterns (PAMPs)?

    <p>Pattern recognition receptors (PRRs)</p> Signup and view all the answers

    What distinguishes the sites of T and B cell activation in the immune response?

    <p>Activation occurs in specific inductive sites like MALT/SALT</p> Signup and view all the answers

    Study Notes

    Immunity to Infection

    • Infectious diseases annually cause 14 million human deaths, caused by six pathogens
      • Extracellular bacteria
      • Intracellular bacteria
      • Viruses
      • Parasites
      • Fungi
      • Prions
    • Infection occurs when an organism successfully avoids innate defenses, colonizing a niche.
    • A biological "horse race" or "war" between pathogen and immune system. The pathogen tries to replicate and expand, while the immune system attempts to eliminate it.
    • A pathogen damages the host only if its replication is detectable clinically.
    • Bacterial toxins can cause disease even without colonization.
    • Immunopathic damage results when host tissues are unintentionally harmed by the immune response.
    • Innate and adaptive effector mechanisms are best suited to pathogens with particular lifestyles and replication modes.

    Host-Pathogen Encounters

    • Innate defense mechanisms help combat pathogens.
    • First obstacle for invaders is intact skin and mucosa. A breach allows pathogen access to sub-epithelial tissues.
    • Compromised immune systems (from disease or treatment) invite opportunistic pathogens.
    • Invasive pathogens can enter the body even with intact surface defenses.
    • Pathogens gain access to mucosae, possibly through M cells or by binding to host surface molecules initiating internalization.

    Host-Pathogen Encounters (continued)

    • A pathogen penetrating skin or mucosa initiates influx of acute phase proteins, pro-inflammatory cytokines (IL-1, TNF, IL-6), and complement components.
    • Coating pathogens with C3b or mannose-binding lectin facilitates removal via alternate/lectin complement cascades.
    • Cellular innate defense is mediated by PRRs of resident DCs, neutrophils, other granulocytes, macrophages, NK cells, γδ T cells, and NKT cells.
    • These PRRs include TLRs, NLRs, RLRs, CLRs, scavenger receptors, cell-bound collectins, and antigen recognition receptors of NK, NKT, and γδ T cells.
    • Soluble collectins in the extracellular matrix activate complement or stimulate phagocytosis, activated by PRR engagement to eliminate pathogens.
    • Leukocytes eliminate pathogens or infected cells by endocytosis/phagocytosis, or by secreting cytotoxic cytokines or perforin/granzyme-mediated cytotoxicity.
    • Also produces toxic NO and ROIS.
    • Chemokines draw neutrophils and leukocytes to infection sites.
    • In blood infections, neutrophils and monocytes provide innate defenses. Organisms reaching the liver or spleen face resident macrophages.
    • Innate response proceeds: local DCs (after maturation due to pathogen components) present pMHCs to naïve T cells, triggering the adaptive immune response.
    • T and B cell activation occur in inductive sites (MALT/SALT), and effector cells migrate to effector sites.
    • Systemic response if mature DCs move to draining lymph nodes or spleen.

    Immunity to Extracellular Bacteria

    • Extracellular bacteria accumulate in interstitial regions (respiratory, urogenital, gastrointestinal tracts, blood).
    • Bacteria often secrete proteins to penetrate/enzymatically cleave mucosal epithelium, gaining access to underlying tissues.
    • Many extracellular bacterial disease symptoms are due to toxins.
    • Exotoxins are actively secreted proteins from Gram-positive or Gram-negative bacteria.
    • Endotoxins are lipid portions of LPS molecules embedded in Gram-negative bacterial walls. They are released when cell walls are damaged, not secreted.
    • A given Gram-negative species may produce both exotoxins and endotoxins.
    • Different exotoxins and endotoxins cause disease via different means and locations.
      • Vibrio cholerae infection causes local exotoxin release, binding to gut epithelial cells, inducing diarrhea.
      • Clostridium botulinum produces neurotoxins that block nerve impulse transmission to muscles, resulting in paralysis.
      • Endotoxin damage to a host is always immunopathic (septic shock).

    Immunity to Extracellular Bacteria (Table)

    • Table 13-1 lists examples of extracellular bacteria and diseases.

    Immunity to Intracellular Bacteria

    • Most intracellular bacteria access the host through breaches in mucosa or skin. Some enter the bloodstream via vectors (ticks, mosquitoes, mites.)
    • Intracellular bacteria evade phagocytes, complement, and antibodies by moving inside host cells.
    • Epithelial and endothelial cells, hepatocytes, and macrophages are popular targets within the host.
    • Dissemination of infection occurs because macrophages are mobile; bacteria that infect them are spread.
    • Intracellular bacteria often enter host cells via clathrin-mediated endocytosis and may remain in a vesicle or escape into the cytoplasm.
    • Intracellular bacteria are usually not very toxic and do not produce tissue-damaging toxins.
    • Intracellular bacteria are hard to eradicate and cause chronic diseases.

    Immunity to Intracellular Bacteria (Table)

    • Table 13-3 lists examples of intracellular bacteria and the diseases they cause.

    Granuloma Formation

    • When intracellular pathogens like Mycobacterium tuberculosis resist CTL killing and hyperactive macrophages, the body walls off the pathogens in granuloma structures around infected macrophages
    • Granuloma has an inner layer with macrophages and CD4+ T cells, while the exterior contains CD8+ T cells.
    • Granulomas may calcify and become fibrotic, with central cell necrosis..
    • In some cases, all pathogens within the dying cells are killed, resolving the infection.
    • In other cases, some pathogens remain viable and dormant within the granuloma, which persists indicating chronic disease.
    • If the granuloma breaks down, trapped pathogens resume replication. Immunosuppression allows pathogens to enter the bloodstream.
    • Cytokines IL-17, IL-12, and IFN-γ (Th1 cells) play roles in granuloma formation
    • IL-4 and IL-10 (Th2 cells) control granuloma formation, damping down inflammation as the bacterial threat is controlled.
    • Bacteria can infect organs causing body widespread damage and death.

    Immune System Evasion by Bacteria (Tables)

    • Tables 13-2 and 13-4 detail immune system elements thwarted by extracellular and intracellular bacteria, respectively, along with the bacteria's methods.

    Next Lecture

    • Chapter 13: Immunity to infection

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    Lecture 29: Immunity to Infection - PDF

    Description

    Explore the critical dynamics of immunity as it combats infectious diseases caused by various pathogens. Understand the roles of innate and adaptive immune responses, the effects of bacterial toxins, and the biological 'war' occurring between pathogens and the immune system. This quiz covers the fundamental concepts of how immunity functions and the challenges faced.

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