Types of Immune Response

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Questions and Answers

What characterizes the pathogenesis of type III hypersensitivity reactions?

Type III hypersensitivity involves the formation of immune complexes from IgG and IgM antibodies binding to soluble antigens, leading to inflammatory reactions and tissue injury.

What is the time frame for the onset of systemic immune complex-mediated diseases in type III hypersensitivity?

Symptoms typically occur 6-8 days after exposure to the foreign serum or antigen.

In type IV hypersensitivity, what is the primary immune cell type involved in the reaction?

The primary immune cells involved are T lymphocytes.

How does type IV hypersensitivity differ from types I, II, and III hypersensitivity?

Type IV hypersensitivity is cell-mediated and occurs after a delay, unlike the other types which are primarily antibody-mediated. Signup and view all the answers

What is the clinical manifestation of the Arthus reaction?

The Arthus reaction manifests as localized immune complex-mediated vasculitis leading to tissue necrosis at the injection site. Signup and view all the answers

What types of antibodies are primarily involved in the pathogenesis of type III hypersensitivity?

IgG and IgM antibodies are primarily involved in type III hypersensitivity reactions. Signup and view all the answers

Describe the role of complement fixation in type III hypersensitivity reactions.

Complement fixation leads to the recruitment of leukocytes, which results in inflammatory reactions and tissue damage. Signup and view all the answers

What are common diseases associated with type III hypersensitivity?

Common diseases include serum sickness and other immune complex-mediated conditions such as systemic lupus erythematosus. Signup and view all the answers

What leads to the delayed response in type IV hypersensitivity reactions?

The delayed response results from the time required for T lymphocytes to proliferate and mediate immune responses after antigen exposure. Signup and view all the answers

How does the tissue injury occur in type III hypersensitivity reactions?

Tissue injury in type III hypersensitivity occurs due to the deposition of immune complexes in postcapillary venules, triggering inflammatory responses. Signup and view all the answers

What role do CD4 T-helper cells play in delayed hypersensitivity reactions?

CD4 T-helper cells (Th1 and Th17) activate macrophages and mediate the inflammatory response against persistent intracellular antigens. Signup and view all the answers

Describe the Mantoux test and its significance in diagnosing tuberculosis.

The Mantoux test involves injecting a purified mycobacterial antigen into the skin, causing a cutaneous reaction within 24 to 48 hours, which indicates prior sensitization to tuberculosis. Signup and view all the answers

Explain how granuloma formation occurs in the context of tuberculosis.

Granuloma formation in tuberculosis is mediated by CD4 T-helper cells that release cytokines like IFN-γ, leading to macrophage activation and transformation to epithelioid cells. Signup and view all the answers

What is the function of Th17 cells in the inflammatory response?

Th17 cells secrete cytokines such as IL-17 and IL-22, which recruit neutrophils and monocytes, promoting inflammation in response to fungal infections. Signup and view all the answers

Discuss the mechanism involved in allergic contact dermatitis.

Allergic contact dermatitis is mediated by CD4 T-helper cells reacting against haptens, such as those from poison ivy, causing an inflammatory skin response. Signup and view all the answers

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

CD8 T cells induce apoptosis in antigen-bearing cells, such as virus-infected or malignant cells, through cytotoxic mechanisms. Signup and view all the answers

What role do cytotoxic T cells play in type-1 diabetes?

Cytotoxic T cells destroy pancreatic islet cells, leading to insulin deficiency and the development of type-1 diabetes as an autoimmune condition. Signup and view all the answers

Describe graft-versus-host disease and its underlying mechanism.

Graft-versus-host disease occurs when transplanted immune cells attack the recipient's tissues due to the activation of CD8 T cells against foreign antigens. Signup and view all the answers

How is chronic transplant rejection characterized at the immune level?

Chronic transplant rejection involves a gradual, immune-mediated destruction of the transplant tissue, often driven by CD8 T cells responding to the donor antigens. Signup and view all the answers

Identify the main inflammatory cytokines involved in macrophage activation.

Key inflammatory cytokines include IFN-γ, IL-3, and GM-CSF, which stimulate macrophage activation and transformation. Signup and view all the answers

Study Notes

Types of Immune Response

Hypersensitivity reactions are categorized into types I-IV.
Type III hypersensitivity is immune complex-mediated.
It is mediated by IgG and IgM antibodies against soluble antigens (exogenous or endogenous), occurring 3-8 hours after exposure.
Reactions can be localized or systemic.
Antigen-antibody complexes form and deposit in postcapillary venules.
Complement fixation leads to leukocyte recruitment, inflammation, necrotizing vasculitis, and tissue injury.
Examples include serum sickness (an acute, self-limited disease following foreign serum injection), and localized reactions like the Arthus reaction (localized immune reaction causing tissue necrosis after antigen injection).

Type IV Hypersensitivity

Also known as cell-mediated or delayed hypersensitivity.
A T lymphocyte-mediated destruction of cells, along with dendritic cells, macrophages, and cytokines.
Occurs 24−48 hours after antigen contact (delayed).
Unlike types I-III, it is not antibody-mediated, but cell-mediated.
This reaction is against persistent, non-degradable intracellular antigens.
Activated by CD4+ T-helper cells (Th1 or Th17).
Leads to the release of inflammatory mediators (e.g., IFNγ, IL-17).
Macrophage transformation, leading to granuloma formation.
Examples: tuberculin reaction (Mantoux test), granuloma formation (e.g., tuberculosis), fungal infection (mediated by Th17 cells), and allergic contact dermatitis.

CD8+ Cell-Mediated Cytotoxic Reaction

Mediated by CD8+ T cells (cytotoxic T cells).
Activated cytotoxic cells induce antigen-bearing cell apoptosis.
Examples:
- Cytotoxic reactions against virus-infected cells and malignant cells.
- Type 1 diabetes (killing of pancreatic islet cells).
- Transplant rejection and graft-versus-host disease.

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Description

This quiz covers various types of immune responses, focusing on hypersensitivity reactions categorized into types I-IV. You'll learn about the mechanisms involved, such as IgG and IgM mediation and the role of T lymphocytes in type IV hypersensitivity. Explore examples like serum sickness and the Arthus reaction to understand localized and systemic reactions.