Types of Immune Response: Hyperreactivity Types III & IV
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Questions and Answers

What is the primary mechanism underlying Type III hypersensitivity reactions?

It is mediated by IgG and IgM antibodies against soluble antigens, leading to the formation of immune complexes.

How does the timing of Type III hypersensitivity reaction differ from Type IV?

Type III reactions occur 3-8 hours after exposure, whereas Type IV reactions begin 24-72 hours later.

Identify a clinical example of a systemic disease associated with Type III hypersensitivity.

Serum sickness is a systemic disease caused by Type III hypersensitivity.

What characterizes the Arthus reaction in localized Type III hypersensitivity?

<p>The Arthus reaction is characterized by a localized immune response causing tissue necrosis at the injection site.</p> Signup and view all the answers

Describe the role of T lymphocytes in Type IV hypersensitivity reactions.

<p>T lymphocytes mediate the destruction of cells in Type IV hypersensitivity, often along with macrophages and cytokines.</p> Signup and view all the answers

What type of tissue injury is primarily observed in Type III hypersensitivity reactions?

<p>necrotizing vasculitis and fibrinoid necrosis are key features of tissue injury in Type III hypersensitivity.</p> Signup and view all the answers

Name a favored site for immune complex deposition in autoimmune diseases related to Type III hypersensitivity.

<p>Renal glomeruli are a favored site for immune complex deposition in autoimmune diseases.</p> Signup and view all the answers

What is the typical latency period associated with Type IV hypersensitivity reactions?

<p>Type IV hypersensitivity reactions typically have a latency period of 24 to 72 hours after antigen exposure.</p> Signup and view all the answers

Explain the inflammatory infiltrate observed in Type III hypersensitivity reactions.

<p>Inflammatory infiltrate typically includes neutrophils in tissues affected by Type III hypersensitivity.</p> Signup and view all the answers

What is one distinguishing feature that separates Type III and Type IV hypersensitivity reactions?

<p>One distinguishing feature is that Type III reactions involve soluble antigens and immune complexes, while Type IV reactions are mediated by T cells.</p> Signup and view all the answers

What distinguishes Type IV hypersensitivity from the other types?

<p>Type IV hypersensitivity is cell-mediated and involves a delayed reaction, unlike the antibody-mediated responses of the first three types.</p> Signup and view all the answers

What role do CD4+ T-helper cells play in Type IV hypersensitivity?

<p>CD4+ T-helper cells activate macrophages and release inflammatory mediators, leading to delayed hypersensitivity reactions.</p> Signup and view all the answers

Describe the Mantoux test and its significance.

<p>The Mantoux test involves injecting a mycobacterial antigen into the skin, resulting in a detectable reaction within 24 to 48 hours, indicating prior exposure to tuberculosis.</p> Signup and view all the answers

What is granuloma formation and why does it occur in Type IV hypersensitivity?

<p>Granuloma formation is the aggregation of epithelioid cells due to persistent intracellular antigens that stimulate T cells unable to eliminate the pathogen.</p> Signup and view all the answers

What are epithelioid cells and their characteristics?

<p>Epithelioid cells are transformed macrophages with abundant, large, and pink cytoplasm, resembling epithelial cells.</p> Signup and view all the answers

How do CD8+ T cells contribute to cell-mediated cytotoxic reactions?

<p>CD8+ T cells mediate cytotoxicity by inducing apoptosis in antigen-bearing cells.</p> Signup and view all the answers

Can you provide examples of conditions associated with CD8+ mediated cytotoxic reactions?

<p>Examples include cytotoxic reactions against virus-infected cells, transplant rejections, and Type 1 diabetes.</p> Signup and view all the answers

What leads to chronic graft-versus-host disease?

<p>Chronic graft-versus-host disease arises from the activation of T cells against host tissues post-transplant, leading to prolonged immune responses.</p> Signup and view all the answers

Explain the significance of allergic contact dermatitis in the context of Type IV hypersensitivity.

<p>Allergic contact dermatitis represents a specific type IV hypersensitivity reaction triggered by environmental chemicals causing skin inflammation.</p> Signup and view all the answers

What pathological changes are observed in the skin during allergic contact dermatitis?

<p>The skin shows epidermal necrosis, inflammation, rashes, and blisters during allergic contact dermatitis.</p> Signup and view all the answers

Study Notes

Types of Immune Response: Types III and IV Hypersensitivity Reactions

  • Type III Hypersensitivity: Mediated by IgG and IgM antibodies against soluble antigens (exogenous or endogenous). Symptoms appear 3-8 hours after exposure.
  • The antigen binds to the antibody, forming an immune complex.
  • Circulating immune complexes deposit in postcapillary venules, leading to complement activation and leukocyte recruitment.
  • Inflammatory reactions, necrotizing vasculitis, and fibrinoid necrosis result.
  • Clinical Examples:
    • Systemic Immune Complex Disease (e.g., Serum Sickness): An acute, self-limited condition occurring 6-15 days after injection of foreign serum (e.g., anti-serum). Characterized by fever, skin rash, arthralgia, vasculitis, and acute glomerulonephritis.
    • Localized Immune Complex Diseases (e.g., Arthus Reaction): A localized immune reaction-induced vasculitis from local tissue necrosis after antigen injection in sensitized individuals.
    • Autoimmune Diseases: Many autoimmune conditions are mediated by this type of hypersensitivity.
  • Favored sites of immune complex deposition: Renal glomeruli, joints, skin, heart, serosal surfaces, and small blood vessels.
  • Microscopically: Necrotizing vasculitis.

Type IV Hypersensitivity (Cell-Mediated)

  • Also known as delayed-type hypersensitivity, it's a T-lymphocyte-mediated response.
  • Occurs 24-72 hours after antigen exposure.
  • Characterized by the destruction of cells (along with dendritic cells, macrophages, and cytokines).
  • Distinguished by:
    • Antibody-Independent Reaction: Unlike Types I, II, and III, Type IV hypersensitivity does not involve antibodies directly.
    • Delayed Onset: Symptoms appear after 24–72 hours, in contrast with types I, II, and III.
    • Cellular Mechanism: Initiated by T lymphocytes.
  • CD4+ T-Cell-Mediated Inflammation:
    • Activated by persistent non-degradable intracellular antigens.
    • CD4+ T helper cells release inflammatory mediators (e.g., IFN-γ).
    • Macrophages transformation to epithelioid cells, and granuloma formation can result.
  • Examples:
    • Mantoux Test (Tuberculin Reaction): Detects exposure to Mycobacterium tuberculosis. Purified mycobacterial antigen induces a delayed-type hypersensitivity reaction in a previously exposed individual.
    • Granuloma Formation: Chronic stimulation of pathogen-specific T cells in response to intracellular pathogens that cannot be eliminated by macrophages.
    • Histopathologic Picture: Microscopic aggregation of epithelioid cells, frequently surrounded by a layer of lymphocytes. Multinucleated giant cells can form in some circumstances. Transformed macrophages called epithelioid cells form large, pink cytoplasm.

Cytotoxic Reactions(Type IV)

  • CD8+ Cell-Mediated Cytotoxic Reaction: Involves CD8+ T cells directly destroying cells presenting the specific antigen.
  • Examples: Cell-mediated destruction of virus-infected cells, transplanted organs and tumor cells.
    • Type 1 Diabetes mellitus: Destruction of pancreatic islet cells by cytotoxic T cells leads to insulin deficiency.
    • Graft-versus-host disease: Immune system of the transplant recipient targets the donor tissues.
    • Chronic transplant rejection: The immune system attacks transplanted organs.
    • Allergic Contact Dermatitis: Environmental chemicals, metals, or topical medications trigger epidermal necrosis and inflammation.

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Types of Immune Response 3 and 4 PDF

Description

This quiz covers Type III and IV hypersensitivity reactions, focusing on the role of IgG and IgM antibodies in immune complexes. You will learn about various clinical examples, symptoms, and the biological mechanisms behind these hypersensitivity types. Test your understanding of these critical immune responses.

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