Hypersensitivity Flashcards
(20 cards)
What are the four types of hypersensitivity reactions?
Type I: Immediate (IgE-mediated)
Type II: Antibody-mediated cytotoxic
Type III: Immune complex–mediated
Type IV: Delayed-type (T-cell–mediated)
Which hypersensitivity is responsible for anaphylaxis, asthma, and hay fever?
Type I (IgE-mediated)
What immune cells are central in Type I hypersensitivity
Mast cells, basophils, Th2 cells, eosinophils
Name key cytokines in Type I hypersensitivity.
IL-4 (IgE class switching), IL-5 (eosinophils), IL-13 (mucus, inflammation)
What is the hygiene hypothesis?
Lack of microbial exposure in childhood skews immune response toward Th2/allergy
What is the counter-regulation hypothesis?
Balanced exposure to microbes may suppress both Th1 and Th2 autoimmune/allergic diseases
What causes tissue damage in Type II hypersensitivity?
IgG/IgM binding to cell-surface antigens → complement activation, ADCC, or phagocytosis
Give 3 examples of Type II hypersensitivity diseases.
Graves’ disease
Myasthenia gravis
Autoimmune hemolytic anemia
What is the main mechanism in Type III hypersensitivity?
Immune complex (Ag–Ab) deposition → complement activation → inflammation
Name 2 diseases caused by Type III hypersensitivity.
Ssickness, systemic lupus erythematosus (SLE), post-streptococcal glomerulonephritis
What is the Arthus reaction
Localized Type III reaction from repeated antigen exposure → immune complex at injection site
What mediates Type IV hypersensitivity?
T lymphocytes (CD4+ Th1 or CD8+ cytotoxic T cells
: How long does a Type IV hypersensitivity reaction take to appear?
24–72 hours (delayed onset)
Name 3 Type IV hypersensitivity examples
Contact dermatitis (nickel, poison ivy)
Tuberculin skin test (Mantoux)
Coeliac disease
What happens in coeliac disease at the immune level
Gliadin (gluten) is modified → presented by HLA-DQ2/8 to CD4+ T cells → mucosal damage
What causes keratinocyte apoptosis in SJS/TEN?
What causes keratinocyte apoptosis in SJS/TEN?
What role do eosinophils play in allergies?
: Kill parasites but in allergy, they degranulate and cause tissue damage (IL-5 driven)
What lab tests help diagnose Type I hypersensitivity?
Total IgE
Allergen-specific IgE (RAST)
Skin prick test
What is the treatment for anaphylaxis
Intramuscular epinephrine (adrenaline)
What is the difference between Type I and IV hypersensitivity
Type I: Immediate, antibody (IgE)-mediated
Type IV: Delayed, T-cell–mediated
