30 Questions
Which cell type plays a role in adaptive immunity by releasing compounds that mediate responses to helminths and allergic disease?
Mast cells
What is the role of Fc-epsilon receptors in IgE-mediated immunity?
Facilitate binding of IgE to mast cells
Which type of hypersensitivity reaction is associated with tissue damage and possible death?
Type I
What is the primary function of the immune response?
Provide rapid and regulated responses to infectious agents
Which type of foreign substance can activate the immune system?
Non-microbial foreign substances
What is the inherit ability in the context of hypersensitivity reactions?
Differentiate self vs. foreign
What is the one sentence summary of hypersensitivity reactions?
Kill pathogens, do not harm the host
Which type of contact dermatitis is often an occupational disease?
Irritant contact dermatitis
What is a key requirement for sensitization in allergic contact dermatitis?
Patch testing
Which cell types are involved in the formation of tissue granuloma?
Macrophages
In which type of reaction is the allergen specific?
Allergic
What type of damage is caused by the size and location of granuloma?
Tissue destruction
Which type of contact dermatitis follows soon after removal of the irritant?
Irritant contact dermatitis
What is the tissue origin of the cell types involved in tissue granuloma?
Macrophages
Which type of contact dermatitis may take some time for the resolution of symptoms?
Allergic contact dermatitis
In which type of contact dermatitis is a history of contact with the potential chemical key to diagnosis?
Irritant contact dermatitis
What is atopy?
A genetically determined state of hypersensitivity to common environmental allergens
What characterizes Type I hypersensitivity?
IgE activation of mast cells leading to rapid release of inflammatory mediators
What is the major clinical feature of anaphylaxis?
Respiratory, cardiovascular, skin, gastrointestinal, and hematological symptoms
What happens upon first exposure to an allergen in atopic individuals?
Sensitization and formation of IgE antibodies that bind to mast cells and basophils
What is the most common clinical expression of atopic hypersensitivity?
Allergic rhinitis
What are allergens?
Antigens that cause allergies
What characterizes Type II hypersensitivity?
Antibody-mediated injury to tissues, mainly involving IgG antibodies and autoimmune diseases
Which type of hypersensitivity reaction is cell-mediated and typically shows a 2-7 day delay with minimal tissue damage and a large influx of macrophages?
Type IV
Which clinical situation is a Type III hypersensitivity reaction characterized by symptoms such as fever, weakness, rashes, and edema?
Serum sickness
What are the clinical situations associated with Type II hypersensitivity reactions?
Incompatible blood transfusion reactions
What is the characteristic skin reaction used to indicate a positive tuberculin skin test?
Induration
Which type of hypersensitivity reaction involves immune complex mediated inflammation and tissue damage?
Type III
What is the characteristic feature of allergic contact dermatitis?
Pruritic papules and vesicles on an erythematous base
What is the mechanism behind the skin reaction in allergic contact dermatitis upon exposure to the same allergen?
Activation of memory T-cells
Study Notes
Hypersensitivity Reactions: Types and Clinical Situations
- Type II hypersensitivity clinical situations include incompatible blood transfusion reactions, hemolytic disease of the newborn, autoimmune hemolytic anemias, and autoimmune diseases.
- Type III hypersensitivity is immune complex mediated and can lead to inflammation and tissue damage when immune complexes are formed in excess and deposit in tissue and blood vessel walls.
- Type III hypersensitivity clinical situations include persistent infections like malaria, leprosy, autoimmune diseases such as SLE and dermatomyositis, and inhaled antigens like Farmer's lung and bronchopulmonary aspergillosis.
- Symptoms of serum sickness, a type III hypersensitivity clinical situation, include fever, weakness, rashes, and edema.
- Type IV hypersensitivity, also known as Delayed Type Hypersensitivity (DTH), is cell-mediated and typically shows a 2-7 day delay with minimal tissue damage and a large influx of macrophages.
- Type IV hypersensitivity reactions include allergic contact dermatitis, tuberculin skin test, DTH associated with autoimmunity, and granulomatous disease.
- Allergic contact dermatitis is characterized by skin inflammation, pruritic papules, and vesicles on an erythematous base, and can be caused by allergens like nickel, preservatives, dyes, and fragrances.
- Allergic contact dermatitis begins when a contact allergen enters the skin and is taken up by antigen-presenting Langerhans cells, which then activate allergen-specific T cells in the skin to release inflammatory cytokines.
- Skin eruptions in allergic contact dermatitis appear as erythema, swelling, vesiculation, blistering, scaling, and weeping, and are typically pruritic.
- Patch testing for allergic contact dermatitis is based on the memory response, where antigen-specific memory T-cells in the skin are activated upon exposure to the same allergen, leading to a positive reaction.
- Tuberculin skin test is used for screening for tuberculosis by injecting PPD intradermally and reading the skin reaction 48-72 hours later, with a positive test indicated by induration.
- Candida normally lives on the skin and inside the body without causing problems, and poison ivy-induced contact dermatitis involves a CD8+ CTL response.
Test your knowledge of hypersensitivity reactions with this quiz covering type II, type III, and type IV hypersensitivity, including clinical situations, symptoms, and specific examples such as allergic contact dermatitis and tuberculin skin test.
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