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
What is type III hypersensitivity known as?
Complex-mediated hypersensitivity
Type III hyper components?
○ IgG and IgM directed against a soluble antigen
○ Small antigen–antibody complexes precipitate out and deposit in tissues
Arthus Reaction
○ Skin reaction caused by type III hypersensitivity
○ Localized inflammation characterized by redness and edema
Serum Sickness
○ Generalized type III hypersensitivity reaction
○ passive immunization of humans with animal serum
○ Produces antibodies against the foreign animal proteins in patients
Laboratory Testing for Type III hyper
○ Testing for ANAs
○ Fluorescent staining of tissue sections to detect deposited immune complexes
○ Testing for rheumatoid factor (an anti-IgG)
○ Testing complement levels
What happens to complement levels in Type III Hyper
May be decreased in the serum during periods of high disease activity
What is Type IV Hypersensitivity known as?
Cell-mediated hypersensitivity
What are the key components of Type IV Hyper?
Th1 cells and macrophages are involved
What are the 4 steps in Type IV Hyper?
○ APCs present antigen to naïve T helper cells, which differentiate into Th1 cells
○ Th1 cells release cytokines that attract and activate macrophages
○ Macrophages induce inflammation
○ Cytotoxic T lymphocytes are recruited and destroy target cells
How long does it take for Type IV Hyper to peak?
48 to 72 hours after antigen exposure
Clinical Examples of Type IV Hypersensitivity
○ Infections with intracellular pathogens
○ Contact dermatitis
○ Hypersensitivity pneumonitis
Hypersensitivity pneumonitis
○ Allergic diseases of the lungs
○ Caused by inhalation of bacterial and fungal spores
Contact Dermatitis
○ Low-molecular-weight compounds contact the skin and act as haptens to sensitize Th1 cells
○ Skin eruptions with erythema, swelling, and papules are produced
Contact Dermatitis examples
○ poison ivy
○ poison oak
○ nickel salts
○ materials in cosmetics and hair dyes
○ Latex
Skin Testing for Delayed Hypersensitivity
○ Patch test
○ Mantoux method
Patch test
○ Antigen applied to skin surface
○ Test for contact dermatitis
○ (+) test = redness with papules or tiny blisters
Mantoux method
○ Antigen injected intradermally
○ Test for tuberculosis exposure (PPD) or T-cell function
○ (+) test = induration
