Immunology: Persistent Infections and Hypersensitivity
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Questions and Answers

What immune reaction is often evoked by persistent infections with certain microorganisms?

  • Delayed-type hypersensitivity (correct)
  • Autoimmunity
  • Immediate hypersensitivity
  • Anaphylaxis

    • What is a common outcome of unresolved acute inflammation?

  • Chronic inflammation (correct)
  • Systemic shock
  • Immediate recovery
  • Granulomatous reaction

    • Which disease is an example of an autoimmune disease resulting from chronic inflammation?

  • Silicosis
  • Bronchial asthma
  • Rheumatoid arthritis (correct)
  • Inflammatory bowel disease

    • Chronic inflammation can occur as a result of which factor?

    <p>Unregulated immune responses against microbes</p> Signup and view all the answers

    What morphological pattern can be seen in diseases characterized by chronic inflammation?

    <p>Mixed acute and chronic inflammation</p> Signup and view all the answers

    Which of the following substances could potentially lead to chronic inflammation when exposure is prolonged?

    <p>Particulate silica</p> Signup and view all the answers

    In which condition does chronic inflammation contribute to disease despite not being conventionally considered inflammatory?

    <p>Alzheimer's disease</p> Signup and view all the answers

    What is a potential consequence of chronic inflammation on tissue?

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

    What role do macrophages primarily play in chronic inflammation?

    <p>Secreting mediators of inflammation and promoting tissue repair</p> Signup and view all the answers

    What characterizes classical macrophage activation?

    <p>Production of reactive oxygen species and nitric oxide</p> Signup and view all the answers

    Which of the following is NOT a function of alternatively activated macrophages?

    <p>Killing ingested microbes directly</p> Signup and view all the answers

    How do monocytes migrate to tissues during inflammation?

    <p>By adhering to blood vessel walls and extravasating</p> Signup and view all the answers

    What is the primary source of tissue-resident macrophages?

    <p>Fetal liver and yolk sac during early development</p> Signup and view all the answers

    What distinguishes M1 macrophages from M2 macrophages?

    <p>M2 macrophages are involved in immune suppression</p> Signup and view all the answers

    What is the half-life of blood monocytes?

    <p>About 1 day</p> Signup and view all the answers

    What is one of the key roles of macrophages in chronic inflammation?

    <p>Stimulating the formation of new blood vessels</p> Signup and view all the answers

    Which of these cells are considered a type of macrophage?

    <p>Kupffer cells</p> Signup and view all the answers

    What triggers the classical pathway of macrophage activation?

    <p>Engagement of toll-like receptors by microbial products</p> Signup and view all the answers

    What principle role do macrophages play in the immune system?

    <p>Removing damaged tissues and pathogens</p> Signup and view all the answers

    Which cytokine is crucial for classical macrophage activation?

    <p>IFN-gamma</p> Signup and view all the answers

    In which condition do macrophages primarily contribute to tissue injury?

    <p>Chronic inflammation</p> Signup and view all the answers

    What mechanism ensures the emigration of monocytes into tissues?

    <p>Adhesion molecules and chemotactic factors</p> Signup and view all the answers

    What is one of the hallmarks of chronic inflammation resulting from macrophage activity?

    <p>Tissue destruction</p> Signup and view all the answers

    Which cytokine is primarily produced by TH1 cells to activate macrophages?

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

    What is referred to as tertiary lymphoid organs in chronic inflammation?

    <p>Clusters of lymphocytes resembling lymph nodes</p> Signup and view all the answers

    Which type of T lymphocyte is primarily involved in allergic inflammation and defense against helminths?

    <p>TH2</p> Signup and view all the answers

    How do eosinophils contribute to tissue damage in allergic reactions?

    <p>Releasing major basic protein that lyses epithelial cells</p> Signup and view all the answers

    Which of the following statements about B lymphocytes in chronic inflammation is true?

    <p>They cluster with other immune cells at inflammation sites.</p> Signup and view all the answers

    Which cells are characterized by their ability to secrete various cytokines and often participate in both acute and chronic inflammation?

    <p>Mast cells</p> Signup and view all the answers

    What role do chemokines play in chronic inflammation?

    <p>They attract immune cells to the sites of inflammation.</p> Signup and view all the answers

    Which cells interact bidirectionally with lymphocytes to propagate chronic inflammation?

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

    Which cytokines are mainly produced by activated macrophages to promote leukocyte recruitment?

    <p>TNF and IL1</p> Signup and view all the answers

    What happens to macrophages if the irritant that causes chronic inflammation is eliminated?

    <p>They may either die off or migrate out of the area.</p> Signup and view all the answers

    Which cell type primarily promotes allergic reactions by releasing histamine?

    <p>Mast cells</p> Signup and view all the answers

    In chronic inflammation, which cells would be dominant in autoimmune diseases?

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

    Which subset of CD4+ T cells is responsible for recruiting neutrophils to the inflammatory site?

    <p>TH17</p> Signup and view all the answers

    Activated T lymphocytes mainly enhance inflammation through which mechanism?

    <p>Recruiting other immune cells through cytokines</p> Signup and view all the answers

    Study Notes

    Persistent Infections and Inflammatory Reactions

    • Persistent infections by microbes (mycobacteria, viruses, fungi, parasites) trigger delayed-type hypersensitivity (DTH) immune reactions.
    • The inflammatory response may become granulomatous.
    • Acute inflammation can progress to chronic inflammation, like in lung abscesses.

    Hypersensitivity Diseases

    • Chronic inflammation is vital in hypersensitivity diseases, stemming from excessive immune system activation.
    • Autoimmune diseases result from the immune system attacking the body's own tissues.
    • Examples include rheumatoid arthritis and multiple sclerosis.
    • Other cases manifest as unregulated immune responses against microbes like in inflammatory bowel disease.
    • Allergics, like bronchial asthma, are triggered by immune responses against common environmental antigens.
    • Chronic inflammations in these diseases may show combined acute/chronic morphologies with repeated bouts and late-stage fibrosis.

    Prolonged Exposure to Toxic Agents

    • Chronic inflammation arises from protracted exposure to exogenous or endogenous toxic agents.
    • Silica (exogenous) inhalation leads to silicosis (inflammatory lung disease).
    • Atherosclerosis (inflammatory arterial wall disease) is partially attributed to excess cholesterol and lipid deposition.

    Chronic Inflammation Pathogenesis

    • Chronic inflammation links with other disorders not conventionally understood as inflammatory.
    • These include neurodegenerative diseases (e.g., Alzheimer's disease), metabolic syndrome, and some cancers.

    Tissue Destruction and Repair

    • Persistent harmful agents or inflammatory cells cause tissue damage.
    • Connective tissue attempts healing (angiogenesis & fibrosis).

    Cells and Mediators of Chronic Inflammation

    Role of Macrophages

    • Macrophages (mononuclear phagocyte system) are primary cells in most chronic inflammation.
    • Derived from bone marrow hematopoietic stem cells, embryonic yolk sac and fetal liver.
    • Monocytes = circulating precursors; macrophages = tissue cells.
    • Macrophages are widely dispersed in connective tissues, also in specific organs (Kupffer cells in liver, sinus histiocytes in spleen & lymph nodes, microglia in CNS, and alveolar macrophages in lungs).
    • Tissue macrophages have lifespans of months/years; blood monocytes, 1 day.
    • Inflammatory reactions bring monocytes into extravascular tissues, becoming predominant within 48 hours.
    • Two activation pathways: classical (M1) and alternative (M2).

    Classical Macrophage Activation (M1)

    • Induced by microbes, T cell signals (IFN-γ), crystals, and particulates.
    • Produce nitric oxide (NO), reactive oxygen species (ROS), and lysosomal enzymes for microbe killing/tissue injury.
    • Important in host defense but can harm tissues.

    Alternative Macrophage Activation (M2)

    • Induced by IL-4 and IL-13.

    • Suppresses classical pathway.

    • Functions in tissue repair; promotes angiogenesis and collagen synthesis.

    • Macrophages ingest microbes/dead tissues and initiate repair processes (scar formation/fibrosis)

    • Macrophages are critical components of the inflammatory response, secreting cytokines (TNF, IL-1, chemokines) and eicosanoids, which propagate inflammation.

    • macrophages present antigens to T lymphocytes and respond to T cell signals, resulting in a feedback loop to support immune responses.

    Role of Lymphocytes

    • Microbes and antigens activate T and B lymphocytes, amplifying chronic inflammation.
    • T cells (CD4+) are crucial:
      • TH1 produce IFN-γ (activates macrophages)
      • TH2 secrete IL-4, IL-5, IL-13 (activate eosinophils, alt. macrophage activation)
      • TH17 secrete IL-17 (recruit neutrophils/monocytes)
    • T and B lymphocytes, using adhesion molecules & chemokines, migrate to inflammatory sites.
    • Activated macrophages release cytokines that recruit more leukocytes.
    • Activated B lymphocytes & antibody-producing plasma cells also occur in chronic inflammation. Specific antibodies or antibodies to altered tissues can occur. The significance of antibodies in chronic inflammation is uncertain.

    Tertiary Lymphoid Organs

    • Lymphocytes, antigen-presenting cells, and plasma cells aggregate at sites to form lymphoid structures.
    • Occur in long-term rheumatoid arthritis synovium and Hashimoto thyroiditis.

    Other Cells in Chronic Inflammation

    • Eosinophils: Abundant in IgE-mediated reactions & parasitic infections (e.g., eotaxin recruitment). Damaging effect on tissue though beneficial in controlling parasites.
    • Mast cells: Widely distributed in connective tissues; contribute to acute & chronic inflammation and allergic reactions by releasing histamine & prostaglandins.
    • Neutrophils: Found in acute inflammation but can be part of chronic inflammation (months or more). Relevant in chronic bacterial infections (osteomyelitis). Can persist in lung conditions driven by irritants, like smoking.

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    Description

    Explore the complex interactions between persistent infections and hypersensitivity diseases. This quiz covers the mechanisms of inflammation, autoimmune responses, and the impact of prolonged exposure to pathogens on immune reactions. Test your knowledge of chronic inflammation and its implications for diseases like rheumatoid arthritis and asthma.

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