Hypersensitivity Flashcards
What is hypersensitivity
A state of altered reactivity in which the body reacts with an immune response to a foreign agent (e.g., an allergen)
What is an allergen
An antigen that causes an allergic reaction
What is the difference between an allergy and intolerance
Allergy involves the immune system while an intolerance involves the digestive system
What are the 4 types of hypersensitivity
IgE mediated
Cytotoxic responses
Immun complex responses
Cell mediated responses
What is one example of each type of hypersensitivity
1-IgE CUTANEOU ATOPY
2- Cytotoxic HAEMOLYTIC ANAEMIA
3- Immune complex ARTHUS REACTION
4- Cell mediated TUBERCULOSIS
What are haptins
Haptens are small molecules that can be recognized by a specific antibody but cannot elicit an immune response
A hapten must be chemically linked to a protein molecule (carrier) to elicit antibody and/or T-cell responses
What is the most common type of hypersensitivity
type 1
What produces IgE antibody
B cells
What is IgE usually attached to
Basophils
How does IgE produce an allergen response
As the allergens bind to IgE histamine is released from mast cells and basophils
What can cause a production of histamine
Anaphylaxis
Hay fever
Hives
Eczema
Allergies
How are eosinophils and basophils involved in anti-parasitic immunity
Eosiniophils are parasite eaters
Basophils are involved in allergic reactions
How does the immune system react in type 1
T cells recognise foreign antigen and release IL-4 and IL-12 to activate B cells
B cells class switch from producing IgM to IgE after first exposure to allergen
IgE binds to Fc receptor on mast cells or CD63 on basophils
IgE recognises allergen and next exposure binds rapidly and causes immediate degranulation of immune cells (elicitation)
What is atopy
Genetic predisposition
What are examples of cutaneous atopy
Allergic rhinitis (hay fever)
Atopic dermatitis (allergic eczema)
Asthma (lower respiratory tract)
Allergic reaction to chlorhexidine
What is systemic anaphylaxis
Anaphylactic shock
Which hypersensitivity causes anaphylactic shock
Type 1
What produces anaphylatoxins
Complement pathway (classical)
What are the main effects of anaphylactic shock
Respiratory system (narrowing)
Cardiovascular system
What can test for type 1 hypersensitivity
Skin patch test
-Wheal and flare reaction
-Helps to identify the allergen
Blood test
-Measures IgE levels in blood
Oral challenge
-Diagnoses food allergy
What drugs can be used to treat type 1
Anti-histamines – histamine receptor antagonist
Hydrocortisone – block histamine synthesis
Epinephrine – reverses effects of granules (vasoconstriction, relaxes muscles)
What are the possible immunological treatments of type 1
Hypo- or de- sensitisation – injections of allergen
IgE to IgG production
What drives type 1 hypersensitivity
histamine and anaphylatoxins
What happens in type 2 hypersensitivity
Involves activation of complement by antibody (not IgE) binding to an antigen (cell surface auto-antigens or allergens)
Cell is lysed by membrane attack complex formation (complement) and antibody dependent cellular cytotoxicity (NK cells or CD8+ T cells)
When might a type 2 reaction occur
Transfusion of the wrong blood type
What does type 3 hypersensitivity involve
reactions against soluble antigens (or allergens) circulating in blood - activates complement which attracts neutrophils to the site
Antibody-antigen immune complexes are deposited in tissues which leads to immune responses
What causes arthus reaction
Type 3 hypersensitivity
Antibody-antigen complexes are localized in blood vessel walls
Can arise from injected particles (e.g., booster vaccinations) or from inhaled or ingested allergens (e.g., farmers lung)
What is serum sickness
Systemic form of Arthus reaction
Antibody-antigen complexes lodge in many different tissues
What is Oral erythema multiforme
Characterized by blistering of oral mucosa
Deposition of immune complexes (IgM-bound immune complexes) in the oral mucous membrane
Viral or drug-related (hypersensitivity)
Caused by type 3 hypersensitivity
What is type 4 hypersensitivity
T cell-mediated hypersensitivity reaction (no antibodies)
Delayed response (due to recruitment of T cells)
Localized T cell reaction at site of antigen exposure
Involves both CD4+ T cells (damage via macrophages) and CD8+ T cells (direct damage of cells – cytotoxicity)
-Cytokines secreted by T helper cells activate macrophages and cytotoxic T cells
What are examples of type 4
Contact dermatitis
Tuberculosis - granulomasin lung tissue
Oral disease - Orofacial Granulomatous
