Hypersensitivity Type I: Allergy
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Questions and Answers

What is the first stage that an allergy undergoes when the immune system encounters an allergen?

  • Allergen response phase
  • Reactive Phase
  • Sensitisation (correct)
  • Degranulation

Which immune cells are primarily involved in the degranulation process during an allergic reaction?

  • Mast cells and Eosinophils (correct)
  • Basophils and Platelets
  • B cells and T cells
  • Neutrophils and Macrophages

Which of the following describes the physiological response during the reactive phase of an allergy?

  • Gradual sensitisation without symptoms
  • Antigen-based allergic response
  • Complete immune tolerance
  • Immunological and physiological responses (correct)

What typical symptoms are associated with inflammation during an allergic response?

<p>Rubor, Calor, Dulor, Tumour, Loss of function (B)</p> Signup and view all the answers

Which antibody plays a critical role in mediating allergic reactions?

<p>IgE (D)</p> Signup and view all the answers

What primary factor affects the severity of an allergic response?

<p>The concentration of the allergen (C)</p> Signup and view all the answers

Which characteristic differentiates parasitic antigens from allergens?

<p>Presence in high doses (B)</p> Signup and view all the answers

What type of allergic reaction is characterized by symptoms like hives and redness?

<p>Allergic dermatitis (D)</p> Signup and view all the answers

Which cells are involved in amplifying an allergic response?

<p>Mast cells, Eosinophils, Basophils (D)</p> Signup and view all the answers

What causes lower blood pressure during anaphylaxis?

<p>Histamine and TNF-α (A)</p> Signup and view all the answers

Which of the following is NOT a symptom of anaphylaxis?

<p>Abdominal cramps (C)</p> Signup and view all the answers

What dictates the type of allergic reaction experienced?

<p>Concentration and clustering of sensitised nodes (B)</p> Signup and view all the answers

What are the components involved in the symptoms of hives?

<p>TNF, Chemokine, PAF, Heparin, histamine (A)</p> Signup and view all the answers

What is the primary role of IgE in the immune response?

<p>To promote and intensify the immune response until the threat is neutralized. (A)</p> Signup and view all the answers

What genetic factor is primarily involved in increasing the risk of allergies?

<p>Over expression of GATA-3 transcription factor. (A)</p> Signup and view all the answers

Which type of immune cell is primarily associated with allergy responses?

<p>T-helper 2 (Th2) cells. (A)</p> Signup and view all the answers

How does IL-4 affect T-cell differentiation?

<p>It suppresses Th1 differentiation and promotes Th2 differentiation. (C)</p> Signup and view all the answers

What is the outcome of the immune response during an allergic reaction?

<p>A large immune reaction to non-threatening antigens. (B)</p> Signup and view all the answers

Which cytokines are overexpressed in individuals predisposed to allergies?

<p>IL-4, IL-5, IL-9, and IL-13. (C)</p> Signup and view all the answers

What triggers the class switching of B-cells to produce IgE?

<p>Interaction with CD40L and IL-13. (C)</p> Signup and view all the answers

What role do mast cells play in the immune reaction associated with allergies?

<p>They contribute to the degranulation and release of histamines and interleukins. (A)</p> Signup and view all the answers

What is the primary aim of the gastrointestinal response to infection?

<p>To evacuate the cause of infection as quickly as possible (C)</p> Signup and view all the answers

What is NOT a function of leukotrienes and prostaglandins during a gastrointestinal reaction?

<p>Increasing nutrient absorption (D)</p> Signup and view all the answers

Which of the following methods is commonly used to identify potential allergens?

<p>Food diary analysis (B)</p> Signup and view all the answers

What does serum IgE concentration indicate about an individual?

<p>The likelihood of developing allergies (B)</p> Signup and view all the answers

Which factor is NOT considered when determining the severity of an allergic reaction?

<p>Personal hygiene practices (C)</p> Signup and view all the answers

Anaphylaxis is characterized by which of the following responses?

<p>Multi-system response to an allergen (C)</p> Signup and view all the answers

What is the role of specific epitopes in allergy management?

<p>To identify causative allergens (A)</p> Signup and view all the answers

In the context of allergy diagnosis, why is the skin prick test significant?

<p>It identifies specific epitopes from related substances (D)</p> Signup and view all the answers

Flashcards

Atopic Predisposition

A genetically determined tendency to develop allergic reactions, characterized by increased production of IgE antibodies and Th2 cells in response to common allergens.

Th2 Cells

A type of immune cell that promotes the development of allergic responses. Th2 cells release cytokines like IL-4, IL-5, and IL-13, which contribute to IgE production and mast cell activation.

IgE Antibody

A type of antibody that plays a crucial role in allergic reactions. It binds to allergens and triggers the release of histamine and other mediators from mast cells.

Class Switching to IgE

The process of switching from producing one type of antibody (IgG) to another (IgE), which is activated by cytokines and signals from Th2 cells. IgE becomes dominant when there is exposure to a strong allergen.

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Mast Cells

A group of cells that are found in tissues throughout the body, particularly in the skin, lungs, and gastrointestinal tract. When activated by IgE and allergens, they release inflammatory mediators such as histamine, which cause the symptoms of allergic reactions.

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Degranulation

The release of chemicals from mast cells and other immune cells in response to an allergen. These chemicals trigger the symptoms of an allergic reaction.

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Allergic Reaction

A type of reaction that occurs when the immune system overreacts to a harmless substance, such as pollen, food, or insect venom.

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Predisposition to Allergy

The combination of genetic factors and environmental factors that contribute to the development of allergies. These factors can include family history of allergies, exposure to allergens, and certain lifestyle choices.

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Sensitization

The initial exposure to an allergen that primes the immune system but doesn't trigger a reaction.

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Reactive Phase

The second or subsequent exposure to an allergen that triggers a full-blown allergic reaction.

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IgE

A type of antibody that plays a crucial role in allergic reactions. It binds to allergens and triggers the release of inflammatory mediators.

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Cardinal Signs of Inflammation

The hallmark signs of inflammation, including redness (rubor), heat (calor), pain (dolor), swelling (tumor), and loss of function.

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What is an allergen?

Allergens are proteins that trigger an immune response in sensitive individuals, leading to allergic reactions. They are typically present in low doses with high solubility and are stable.

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What is a parasitic antigen?

Parasitic antigens are proteins released by parasites that can also stimulate an immune response, but they are typically present in lower doses and have a shorter lifespan.

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What is anaphylaxis?

Anaphylaxis is a severe, life-threatening allergic reaction that can cause difficulty breathing, lightheadedness, fainting, hives, and redness. It affects multiple body systems.

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What is the difference between a local and systemic allergic reaction?

Local reactions are confined to the area where the allergen enters the body, while systemic reactions affect multiple organs and can be life-threatening.

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What factors determine the severity of an allergic reaction?

The severity of an allergic reaction depends on several factors, including the concentration of the allergen, the amount of IgE present, the location of the allergen exposure, and the individual's sensitivity.

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What dictates the type of allergic reaction?

The type of allergic reaction depends on the location of the allergen exposure and the types of immune cells involved. Histamine release and other inflammatory mediators can trigger a range of symptoms from localized hives to widespread anaphylaxis.

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What causes the symptoms of anaphylaxis?

The symptoms of anaphylaxis are caused by the release of histamine, TNF-α, prostaglandins and heparin, which contribute to changes in vascular permeability, blood pressure, and airway constriction.

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What are the symptoms of anaphylaxis?

The symptoms of anaphylaxis can include difficulty breathing, lightheadedness, fainting, pallor, hives, and redness. These symptoms are caused by the release of various inflammatory mediators that affect different parts of the body.

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Anaphylaxis: Centralized Response

The reaction to an allergen in anaphylaxis affects the entire body (centralized) rather than just the area of contact (localized).

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Gastrointestinal Reactions: Localized Response

The goal is to remove the source of infection quickly. The gut is the focus of the response.

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Leukotrienes and Prostaglandins in Gastro Reactions

Leukotrienes and prostaglandins are chemicals that cause smooth muscle contraction in the gut, leading to diarrhea and vomiting.

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Diarrhea Mechanism

Diarrhea happens when the digestive process speeds up.

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Vomiting Mechanism

Vomiting happens when the stomach muscles contract forcefully, pushing out the contents.

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Skin Prick Test: Epitope Determination

Skin Prick Testing helps determine which specific substances trigger an allergic reaction.

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Serum IgE: Allergy Likelihood

Serum IgE levels can indicate the likelihood of an allergy.

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Assessing Allergy Severity: Clinician's Role

Clinicians use information like previous reactions, allergen stability, and the site of absorption to assess the severity of an allergic reaction.

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Study Notes

Hypersensitivity Type I: Allergy

  • Allergy is a misdirected immune response to a non-threatening antigen.
  • Allergy escalates the immune response to cause a large immune reaction.
  • Allergy has genetic factors that increase the number and reaction potential towards Th2 cells and IgE antibody response.

Predisposition to Allergy (Atopy)

  • Rates of allergy are increasing in Western populations, reaching 40%.
  • Allergy is caused by a propensity towards an immune response involving IgE and Th2 cells.
  • Class switching to IgE in B cells is a key aspect.
  • Th2 cells increase, resulting in two interactions: T-cell differentiation to Th2 cells and B-cells switching to IgE.
  • Overexpression of IL-4, 5, 9, and 13, requiring GATA-3 Transcription Factor, is observed.

Mechanisms of Allergy

  • Sensitization: Initial encounter with allergen creates an immune response that's not overly misdirected.
  • Reactive Phase: Subsequent encounters trigger immunological and physiological responses, including inflammatory signs (rubor, calor, dolor, tumor, loss of function).

IgE Production

  • Th2 cells and naïve B cells interact with CD40, CD40L, and IL-13.
  • IgE is locally produced in germinal centers of lymph nodes.
  • IgE receptors (IgER) are found on basophils, eosinophils, and mast cells.
  • Positive feedback loops intensify IgE response until the threat is neutralized.

Causes of Degranulation in Immune Cells

  • Mast cells release histamine, interleukins, and lipid mediators (leukotrienes, prostaglandins, PAF).
  • The aim of these releases is to attract and activate other immune cells.
  • The outcome of the cascade is an exponential response to stimuli leading to inflammatory responses.

Symptoms of Allergy

  • Tumour: Localized inflamed area with a central flare.
  • Rubor: Red inflammation surrounding the flare.
  • Dolor/Calor: Painful and often itchy, warm, inflamed area.
  • Loss of function: Primarily seen in digestive and respiratory tracts.
  • Inflammation is the primary source of symptoms through several pathways (examples given in presentation)

Types of Allergic Reaction

  • Anaphylaxis: A centralized allergic response.
  • Allergic rhinitis: Symptoms include sneezing and coughing.
  • Diarrhoea and vomiting: Gastrointestinal reaction.
  • Allergic dermatitis (hives): Skin reaction manifest with hives.
  • What determines the type of reaction, and factors include the concentration /site of allergen.

Comparison of Allergens vs. Parasitic Antigens

  • Protein allergens are present in higher doses, have low molecular weight (10-40 kDa), are highly soluble, stable, and bind to MHC class II.
  • Parasitic antigens are present in lower doses, have low molecular weight (10-40 kDa), are highly soluble, have short-acting stability, and mainly bind to MHC class II.

Severity of Allergic Responses

  • High allergen and IgE doses lead to high responses.
  • Amplification of response by mast cells, eosinophils, and basophils.
  • Location of activating nodes dictates location and type of response.

Diagnosis of Allergy

  • Clinicians look for the cause of the reaction, causative substances, specific epitopes, and predict symptom severity.
  • Identifying disease episodes through food diaries (but not ideal for anaphylaxis) is crucial.
  • Skin prick tests and epitope determination (e.g., Der-P1, PR-10, BSA) help identify specific triggers.
  • Serum IgE levels correlate with likelihood and severity of allergic reactions..

Determination of Severity

  • Clinicians need to consider factors like previous reactions; epitope stability and ubiquity; and site of absorption to determine the severity.

Summary

  • The presentation highlights the intricate relationship between immune cells, allergens, and resultant reactions.
  • Different types of allergic reactions affect various parts of the body.
  • The role of laboratories in allergy diagnosis and patient care is crucial, providing vital information.
  • Clinicians and the laboratory collaborate in providing accurate diagnoses and effectively managing patient care.

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Hypersensitivity Type I: Allergy PDF

Description

Explore the mechanisms and genetics behind Type I hypersensitivity in allergies. This quiz covers topics such as genetic predisposition, sensitization, and the roles of IgE and Th2 cells. Understand the processes that lead to allergic reactions and their implications.

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