30 Questions
What is the main cell type implicated in type I hypersensitivity reactions?
Eosinophils
Which mediator is responsible for increased mucus production in the nasal mucosa during hay fever?
Histamine
What is the role of IL-5 in allergic reactions?
Activates eosinophils
In type I hypersensitivity reactions, what prolongs the half-life of IgE antibodies?
FcεR1 binding
What is the primary inflammatory mediator released during the immediate response in type I hypersensitivity reactions?
Histamine
What is the primary difference between hypersensitivity and autoimmunity?
Hypersensitivity refers to the immune system responding aggressively to a normally harmless antigen, while autoimmunity refers to the immune response against self antigens.
Which type of hypersensitivity is characterized by the production of IgE antibodies against environmental antigens?
Type I
What is a common manifestation of immediate hypersensitivity (Type I)?
Vascular leakage and mucosal secretions
How does Type II hypersensitivity differ from Type III?
Type II involves antibody against cell or tissue antigens, while Type III involves antibody against soluble antigens
Which component plays a central role in the development of immediate hypersensitivity?
Th2 cells
What term is used to describe individuals with a propensity to develop immediate hypersensitivity reactions?
Atopic
How do Th2 and IL-4–secreting follicular helper T (Tfh) cells contribute to the development of immediate hypersensitivity reactions?
Stimulate the production of IgE antibodies
What is the primary role of IgE antibodies in Type I Hypersensitivity?
Binding to high affinity FcεR1 on mast cells
In Type I Hypersensitivity, what is the consequence of cross-linking IgE bound to mast cells by the antigen?
Release of mast cell mediators
What is the function of cytokines produced by mast cells and epithelial cells in Type I Hypersensitivity?
Contribute to leukocyte recruitment
How do eosinophils and neutrophils contribute to Type I Hypersensitivity?
Liberate proteases causing tissue damage
What is the immediate consequence of the activation of Th2 and IL-4–secreting Tfh cells in immediate hypersensitivity reactions?
Production of IgE antibodies
What is the main mechanism by which IgG antibodies contribute to inflammation in autoimmune diseases like SLE?
Binding to neutrophils and macrophages, activating them to release ROS and lysosomal enzymes
In systemic lupus erythematosus (SLE), what is the process responsible for the gradual development of broad and destructive antibody responses?
Epitope spreading due to expansion of cellular constituents becoming autoantigens
Which cells are responsible for releasing reactive oxygen species (ROS) and lysosomal enzymes at sites of antibody deposition?
Neutrophils and macrophages
Which system is activated by IgG antibodies in autoimmune diseases like systemic lupus erythematosus (SLE)?
Complement system by the classical pathway
Which hypersensitivity reaction is characterized by the deposition of immune complexes in blood vessels and often manifests as widespread vasculitis, arthritis, and nephritis?
Type III
What is the primary therapy intended to limit inflammation in antibody-mediated diseases like rheumatic fever?
Corticosteroids
In rheumatic fever, what triggers the inflammatory disease characterized by vasculitis, arthritis, and nephritis?
Cross-reactivity between streptococcal antibodies and heart tissues
What is a clinically relevant manifestation of an Arthus reaction in some vaccine recipients who have previously been vaccinated or have antibodies against the vaccine antigen?
Painful swelling at the injection site
Which type of hypersensitivity reaction involves T cell-mediated autoimmune diseases that are usually limited to a few organs and not systemic?
Type IV
How does intravenous IgG (IVIG) therapy potentially work in treating antibody-mediated diseases?
By reducing pathogenic antibody half-life
What is the characteristic manifestation of an Arthus reaction induced by subcutaneous administration of a protein antigen to a previously immunized animal?
Formation of immune complexes at the injection site
What is the major role of antibodies blocking CD40 or its ligand in treating T cell-mediated autoimmune diseases?
Inhibiting B cell activation
Which type of hypersensitivity reaction is induced by systemic administration of a protein antigen and leads to circulating immune complexes formation?
Type III
Study Notes
Hypersensitivity and Autoimmunity
- Hypersensitivity and autoimmunity are examples of an overly aggressive immune system and can overlap.
- Hypersensitivity refers to the immune system responding aggressively to a normally harmless antigen.
- Autoimmunity refers to the immune response against self-antigens.
Types of Hypersensitivity
- Type I: Immediate Hypersensitivity (IgE)
- Mediated by IgE antibodies and mast cells
- Causes rapid vascular leakage and mucosal secretions, followed by inflammation
- Examples: hay fever, food allergies, bronchial asthma, and anaphylaxis
- Type II: Antibody-mediated Hypersensitivity
- Antibodies against cell or tissue fixed antigen
- Can cause damage and activate the complement and ADCC
- Type III: Immune Complex-mediated Hypersensitivity
- Antibodies against soluble antigen complex production
- Immune complexes deposit in blood vessels, causing inflammation and tissue injury
- Type IV: T Cell-mediated Hypersensitivity
- Reactions of T cells, often against self-antigens in tissues
- Examples: autoimmunity and exaggerated or persistent responses to environmental antigens
Immediate Hypersensitivity (Type I)
- Activation of Th2 cells and production of IgE antibody
- IgE binds to high-affinity FcεR1 on mast cells, prolonging its life span
- On subsequent exposure to the antigen, cross-linking of the bound IgE by the antigen
- Release of mast cell mediators (primary inflammatory mediators)
- Recruitment and activation of Th2 response and recruitment of eosinophils and neutrophils
- Release of tissue-damaging chemicals (late response)
Clinical Syndromes of Type I Hypersensitivity
- Hay Fever
- Inhaled allergens cause rhinitis and sinusitis
- Mast cells in the nasal mucosa produce histamine and Th2 cells produce IL-13
- Food Allergy
- Defined as an immune-mediated adverse reaction to food
- Bronchial Asthma
- Anaphylaxis
Role of Innate Immunity in Type I Hypersensitivity
- The innate immune system consists of multiple cell types that express PRRs
- Allergens are frequently found in forms and mixtures that contain PAMPs and DAMPs
- Interaction of allergens with the innate immune system normally results in immune tolerance, but in allergic disease, it induces recurring and/or chronic inflammation and loss of immunologic tolerance
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