Hypersensivity Flashcards
What are the four types of hypersensitivity?
Type I, Type II, Type III, Type IV
What is hypersensitivity?
Any inappropriate or excessive immune response that results in bystander damage to the self
Define allergy in the context of hypersensitivity.
Immune responses are induced against innocuous exogenous antigens
What is autoimmunity?
A harmful immune response directed against self-antigens
What roles do allergen, IgE, and mast cells play in Type I hypersensitivity?
Allergen triggers the response; IgE binds to allergens; Mast cells degranulate upon allergen exposure
What are the phases of Type I hypersensitivity?
Sensitisation, Early-phase Reaction, Delayed-phase Reaction
What cytokines are produced during sensitization in Type I hypersensitivity?
IL-4 and IL-13
Fill in the blank: Atopy is a ______ to produce IgE antibody in response to environmental allergens.
[genetic predisposition]
Name two common allergens associated with Type I hypersensitivity.
- Pollen
- House dust mite
What is the triple vascular response of Lewis?
Response induced by histamine release during allergic reactions
What are common causes of systemic allergy or anaphylaxis?
- Bee and wasp stings
- Foods
- Latex rubber
- Drugs
True or False: Anaphylactoid reactions are mediated by IgE.
False
What is the role of antibodies in Type II hypersensitivity?
Opsonisation, Complement activation, Toxin neutralisation, Antibody dependent cell mediated cytotoxicity (ADCC), Direct antimicrobial activity
What happens during the early phase reaction in Type I hypersensitivity?
Mast-cell degranulation occurs due to IgE-allergen interaction
What is the mechanism of action for mast cell stabilisers?
Inhibit release of vasoactive mediators
What is allergen immunotherapy (AIT)?
Desensitization treatment involving escalating doses of allergen
What is the pathophysiology of Type III hypersensitivity?
Immune complex formation due to antigen-antibody interactions
Fill in the blank: In Type III hypersensitivity, the antigen-antibody ratio affects ______ formation.
[complex]
What is delayed hypersensitivity (DTH)?
The slowest form of hypersensitivity mediated by T cells, taking 2 to 3 days to develop
Define haptens in the context of hypersensitivity.
Small molecules that elicit an immune response only when attached to a large carrier such as a protein
What are the clinical effects of Type I hypersensitivity?
Can range from mild allergic reactions to severe anaphylaxis
What tests are used to investigate allergic diseases?
- Skin prick tests
- Specific IgE tests
- Component resolved diagnostics
- Challenge tests
- Mast cell tryptase
What is the significance of the European Academy of Allergy and Clinical Immunology’s recommendation for AIT?
At least 3 years of AIT is recommended to achieve long-term benefits
What is the role of Fc receptor bearing cells in Type II hypersensitivity?
Engage in antibody-dependent cell-mediated cytotoxicity (ADCC)
What factors influence the formation of abnormal immune complexes in Type III hypersensitivity?
Antigen-antibody ratio and the presence of specific antibodies
What are the clinical effects of Type II hypersensitivity?
Can lead to conditions such as hemolytic anemia or transfusion reactions
What is the role of Th1 and Th17 cells in Type IV hypersensitivity?
Th1 cells promote cell-mediated immunity; Th17 cells are involved in inflammatory responses
True or False: Type IV hypersensitivity is primarily antibody-mediated.
False
What is the pathophysiology of immune complex formation in Type III hypersensitivity?
Complexes form when antigens bind with antibodies in circulation
What is the slowest form of hypersensitivity mediated by T cells?
Delayed hypersensitivity (DTH)
This type can take 2 to 3 days to develop.
Define haptens in the context of immunology.
Small molecules that elicit an immune response only when attached to a large carrier such as a protein.
The carrier may not elicit an immune response by itself.
What are the two phases of Type IV hypersensitivity?
- Sensitisation phase
- Effector phase
Provide an example of Type IV hypersensitivity.
Nickel hypersensitivity
This is a common example of contact dermatitis.
What is a common condition associated with Type IV hypersensitivity?
Eczema
What diagnostic method is often used for Type IV hypersensitivity?
Patch testing
Contrast the mechanisms of which hypersensitivity types?
Types I, II, III, and IV hypersensitivity.
List the roles in Type I hypersensitivity.
- Allergen
- IgE
- Mast cells
- Inflammatory cells
- Mediators
- Cytokines
What does atopy refer to?
A genetic predisposition to develop allergic diseases.
What are the roles of antibody, complement, Fc receptor bearing cells, and ADCC in which type of hypersensitivity?
Type II hypersensitivity.
What is the pathophysiology of immune complex formation in which type of hypersensitivity?
Localized and systemic Type III hypersensitivity.
What factors are involved in the formation of abnormal immune complexes?
Various immunological factors.
What roles do haptens, carrier proteins, Th1 cells, Th17 cells, antigen presenting cells, and monocytes/macrophages play in which type of hypersensitivity?
Type IV hypersensitivity.
True or False: Type IV hypersensitivity is mainly mediated by mast cells.
False
It is mainly mediated by CD4 T helper cells and CD8 cytotoxic T cells.
What is the most useful investigation in type 1 hypersensitivity?
Skin prick testing.
Which clinical feature would be unusual in acute systemic type 1 hypersensitivity?
Eczematous rash
