Hypersensitivity Flashcards
What are the 4 types of hypersensitivity reactions?
Type I, Type II, Type III, Type IV
What characterizes hypersensitivity reactions?
An inappropriate or exaggerated immune response against antigens or allergens
What types of hypersensitivity reactions are antibody-mediated?
Type I, Type II, Type III
Which type of hypersensitivity is cell-mediated?
Type IV
When does hypersensitivity occur?
On second and subsequent exposures to antigen
What is an allergen?
A substance that causes an allergic reaction
What are examples of allergens?
- Small soluble proteins or glycoproteins
- Dust mite faeces
- Food components (milk, nuts, eggs, fish)
- Insect saliva
- Plant excretions
- Chemicals
- Drugs (e.g. penicillin)
What happens during the first encounter with an allergen in Type I hypersensitivity?
B-cells produce IgE antibodies which stick to mast cells/basophils
What occurs upon second exposure to an allergen in Type I hypersensitivity?
Allergen binds to IgE on mast cells/basophils, leading to degranulation
What cytokines are involved in Type I hypersensitivity?
- TNF
- IL-4
- IL-5
- IL-13
What is atopy?
Genetic tendency to develop allergic diseases
What is the Hygiene Hypothesis?
Inverse relationship between incidence of infectious disease and allergy/autoimmune disease due to less exposure to infections
What characterizes autoimmune diseases?
- Breakdown of immunologic tolerance
- Presence of autoantibodies
- Lymphocyte infiltration into lesions
- Female bias
- Occurs in families
- HLA associations
What is the principal mechanism of tissue injury in Type II hypersensitivity?
Antibody-mediated (cytotoxic) reactions
What are mechanisms of tissue injury in Type II hypersensitivity?
- Opsonization and phagocytosis
- Complement and Fc-mediated inflammation
- Antibody-mediated cellular dysfunction
What are clinical examples of Type II hypersensitivity?
- Incompatible blood transfusions
- Hyperacute graft rejection
- Myasthenia gravis
- Graves disease
- Acute rheumatic fever
What characterizes Type III hypersensitivity?
Mediated by immune complexes formed by antibodies binding to antigens
What are pathologic conditions resulting from Type III hypersensitivity?
- Vasculitis
- Glomerulonephritis
- Arthritis
What happens during Phase I of Type III hypersensitivity?
Antibody and antigen bind to each other forming a complex
What happens during Phase II of Type III hypersensitivity?
- Deposition of antigen-antibody complexes
- Influx of neutrophils
- Complement activation
What is a major disease associated with Type III hypersensitivity?
Systemic Lupus Erythematosus (SLE)
What characterizes Type IV hypersensitivity?
Cell-mediated response involving T cells
What are the two main mechanisms of Type IV hypersensitivity?
- Delayed-type hypersensitivity (CD4 T cells)
- Direct cell cytotoxicity (CD8 T cells)
What are examples of conditions associated with Type IV hypersensitivity?
- Crohn’s disease
- Rheumatoid arthritis
- Multiple sclerosis
- Tuberculosis
What is the time to develop a Type IV hypersensitivity reaction?
48 - 72 hours
What is the main cell type involved in Type I hypersensitivity?
Mast cell (IgE)
What is the fastest type of hypersensitivity reaction?
Type I hypersensitivity
What is the slowest type of hypersensitivity reaction?
Type IV hypersensitivity
