Chapter 14: Hypersensitivity Flashcards
What is hypersensitivty?
Exaggerated immune response to a typically harmless antigen
How many hypersensitivities are there?
4
What sensitivities have and immediate reaction?
Types I-III
Develop minutes to hours after antigen exposure
What sensitivities have delayed reactions?
○ Type IV
○ Develop 24 to 48 hours after antigen exposure
What is a type I Hypersensitivity known as?
anaphylactic hypersensitivity
What is Type I Hypersensitivity thought as?
Allergies since, they commonly occur within minutes after exposure to an allergen
What are the key components of Type I Hyper?
○ IgE
○ Mast cells
○ Basophils
○ Eosinophils
Sensitization Phase: components
○ APCS: process allergens and present them to Th cells
○ Th2: induce production of allergen specific IgE
○ IgE: binds to FceRI receptors on mast cells and basophils
Activation phase
○ Allergen cross-links adjacent cell-bound IgEs
○ Mast cells and basophils degranulate
○ Chemical mediators are released and bind to target organs
○ Allergy symptoms are produced
What are some common allergens?
○ Pollen
○ Mold spores
○ Animal dander
○ Dust mites
○ Insect venom
○ Certain foods (peanuts, shellfish, dairy products)
○ Certain drugs (penicillin)
○ Latex
Clinical Manifestations of Type I Hypersensitivity
○ Rhinitis (“hay fever”)
○ Asthma
○ Food allergies
○ Urticaria (“hives”)
○ Eczema
○ Systemic anaphylaxis- A potentially fatal reaction
Treatments for Type I Hypersensitivity
○ Avoid allergens
○ Drug therapy
○ Monoclonal anti-IgE antibody
○ Allergy immunotherapy (AIT)- in increasing amounts
How is type I Hyper tested?
○ In Vivo Skin Tests
○ Apply a panel of allergens to separate sites on the skin
○ Wait 15 to 20 minutes
What is a positive test for Type I hyper?
wheal and flare at the site of application
RAST
Used to detect IgE to a specific allergen in patient serum
RIST
Used to detect the total concentration of IgE in patient serum
What is Type II Hypersensitivity known as?
antibody-mediated cytotoxic hypersensitivity
What are key components of Type II Hyper?
IgG and IgM directed against a cell surface antigen
What do the key components of Type II Hyper do?
○ Cell destruction
○ Inhibition of cell function
○ Increase in cell function
What causes cell damage in type II Hyper?
Activation of classical pathway of complement and cell lysis
Clinical Examples of Type II Hypersensitivity
○ Transfusion reactions typically
○ Hemolytic disease of the newborn (HDN)
○ Autoimmune hemolytic anemia
○ Goodpasture’s syndrome
○ Hashimoto’s disease
Hemolytic disease of the newborn (HDN)
○ Caused by development of antibodies by a pregnant woman to red blood group antigens
○ usually Rh D, on the RBCs of the fetus
Direct Antiglobulin Test (DAT)
○ Detects RBCs coated with complement components or IgG antibody
○ Positive test = RBC agglutination
○ If positive: test is repeated with mono-specific anti-IgG, anti-C3b, and anti-C3d
Indirect Antiglobulin Test
○ Aka Coombs’ test
○ Tests patient serum for antibodies to RBC antigens
○ Positive test = RBC agglutination
