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Questions and Answers
What type of hypersensitivity reaction is primarily mediated by IgE?
What type of hypersensitivity reaction is primarily mediated by IgE?
Which of the following is a characteristic of Type II hypersensitivity?
Which of the following is a characteristic of Type II hypersensitivity?
Which of the following triggers immediate hypersensitivity reactions?
Which of the following triggers immediate hypersensitivity reactions?
Which phase of immediate hypersensitivity involves the release of mediators from mast cells?
Which phase of immediate hypersensitivity involves the release of mediators from mast cells?
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Which cell type is primarily responsible for the degranulation process during Type I hypersensitivity?
Which cell type is primarily responsible for the degranulation process during Type I hypersensitivity?
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What is the role of IgE in hypersensitivity reactions?
What is the role of IgE in hypersensitivity reactions?
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Which of the following substances is NOT considered an allergen for Type I hypersensitivity?
Which of the following substances is NOT considered an allergen for Type I hypersensitivity?
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In allergic reactions, what immune response is primarily facilitated by TH2 cells?
In allergic reactions, what immune response is primarily facilitated by TH2 cells?
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What is the role of Treg cells in the activation of TH1 and TH2 cells?
What is the role of Treg cells in the activation of TH1 and TH2 cells?
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Which factor is primarily expressed by TH1 cells?
Which factor is primarily expressed by TH1 cells?
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In which scenario would you expect an increased TH1 response?
In which scenario would you expect an increased TH1 response?
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What is a characteristic of the Hygiene Hypothesis related to allergies?
What is a characteristic of the Hygiene Hypothesis related to allergies?
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Which cytokine is responsible for maintaining TH2 cell responses and eosinophil migration?
Which cytokine is responsible for maintaining TH2 cell responses and eosinophil migration?
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What is one of the immediate mediators produced by mast cells during anaphylaxis?
What is one of the immediate mediators produced by mast cells during anaphylaxis?
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Which of the following is NOT a mediator of the early phase response in an allergic reaction?
Which of the following is NOT a mediator of the early phase response in an allergic reaction?
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Which of the following statements about peanut allergies is true?
Which of the following statements about peanut allergies is true?
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Study Notes
Hypersensitivity Reactions (HPS)
- Hypersensitivity (HPS) are excessive immune responses causing damage in reaction to specific antigens.
- Three types of antigens trigger HPS reactions: infectious agents, environmental substances, and self-antigens.
- Influenza virus and chronic hepatitis are examples of infectious agents that can cause HPS.
- Allergies and atopy, such as asthma or rhinitis, result from environmental substances. Dust can trigger IgE production.
- Autoimmune diseases exemplify self-antigens causing HPS.
Types of Hypersensitivity Reactions
- Four major types of HPS reactions are clinically recognized, classified by Coomb's and Gell.
- Type I (Immediate): IgE-mediated.
- Type II (Antibody-Mediated): IgG-mediated (cytotoxic; bound antigen).
- Type III (Immune Complex): IgG-mediated.
- Type IV (Delayed): T cell-mediated.
Immediate Hypersensitivity (Type I): Allergy
- Atopy is an immediate HPS reaction to environmental antigens, mediated by IgE.
- Atopy is inherited and often associated with high IgE levels, synonymous with allergy.
- Common diseases associated with atopy include anaphylaxis, angioedema, urticaria, rhinitis, asthma, and dermatitis/eczema.
- Allergic reactions have two phases: Early and Late-phases.
Allergens
- Allergens are triggering antigens of allergies.
- Some allergens are low molecular weight and prevalent in the environment.
- Allergens can be inhaled (e.g., pollens, fungal spores, house dust mite feces, grass), ingested (e.g., peanuts, fish, eggs, milk), or administered as drugs (e.g., penicillin, cephalosporins) or venoms.
Degranulating Cells
- Mast cells are the primary cells involved in allergic reactions.
- Mast cells are resident in tissues and express IgE receptors (FcER1).
- Cross-linking of IgE by allergens triggers mast cell degranulation, releasing allergy mediators, particularly in the early phase.
- Eosinophils are circulating cells migrating to areas with type I reactions.
- Basophils are circulating cells that can differentiate into mast cells in tissues. Their functions are still being investigated.
Non-Allergic Reactions
- Non-allergic reactions include complement activation during infections and nervous system signals, such as temperature changes.
- These mechanisms can also activate the previously mentioned cells in the body.
Antibody (IgE)
- B cells, co-stimulated by IL-4 secreted by TH2 cells, switch to IgE production.
- IgE binds to FcER1 on mast cells and eosinophils.
- High IgE levels can occur during parasitic infections (e.g., schistosomiasis) and atopy.
- Allergic reactions are often tested for with prick tests and ELISA.
Mediators of Early Phase
- Mast cells, responding to allergen activation release prostaglandins (cyclooxygenase pathway) and leukotrienes (lipoxygenase pathway).
- These mediators cause vasodilation, increased vascular permeability, and a drop in blood pressure (BP).
- Leukotrienes contribute to nasal secretions (in rhinitis/asthma) and smooth muscle contraction in the lungs.
- Histamine, released from skin mast cells, causes swelling and fluid shift.
Mediators of Late Phase
- Eosinophils release peroxidase, major basic protein, and cationic protein, which damage bronchial tissue, leading to chronic inflammation, smooth muscle hypertrophy, and increased mucus secretion.
- TH2 cells release IL-4 and chemokines, promoting chronic allergic inflammation.
Treatment
- Treatment for hypersensitivity reactions is tailored to severity.
- Identify and avoid allergens when possible.
- Medications, including drugs like beta2-adrenergic agonists (e.g., salbutamol), epinephrine, antihistamines, leukotriene receptor antagonists (e.g., montelukast), and corticosteroids, are used.
Desensitization (Immunotherapy)
- Desensitization is most effective for single allergens.
- A single-allergen desensitization involves subcutaneous injections of increasing doses of the allergen, often successful up to 90% of cases.
- Desensitization may involve TH1 stimulation to block allergen attachment to IgE, or T regulatory (Treg) cells inhibiting TH2 responses.
Predisposing Factors
- Allergy prevalence is high in developed countries, with peanut allergies increasing.
- Factors influencing susceptibility to allergy include:
- Atopy trait (a genetic tendency to an exaggerated IgE response that runs in families).
- Several genes influencing allergy susceptibility (polymorphisms, with variations in genes such as IL-4 and FcER1 genes, significantly contributing, with genes from the mother often influencing allergy more so than those from the father).
Hygiene Hypothesis
- The hygiene hypothesis suggests that allergies are influenced by.
- cleaner living conditions or lack of exposure to certain microbes in the environment.
- exposure to mycobacteria, such as those causing tuberculosis (TB), may prevent a TH2-polarized immune response by eliciting a TH1 response that downregulates TH2 responses in individuals living where TB is common.
Latex Allergy
- Latex allergy is detectable by a skin prick test.
Peanut Allergy
- Peanut allergy can result in complications like angioedema.
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Description
Explore the various types of hypersensitivity reactions and their mechanisms. This quiz covers the immune responses, triggers, and classifications of hypersensitivity, providing insights into immediate, antibody-mediated, immune complex, and delayed reactions. Perfect for those studying immunology or related fields.
