Hypersensitivity Reactions Flashcards
Describe hypersensitivity reactions.
An exaggerated immune response to a typically harmless antigen.
How many types of hypersensitivity reactions are there?
Four.
Type I, II, and III hypersensitivity reactions are classified as…
antibody mediated.
Type IV hypersensitivity reaction can be classified as…
sensitized T cells.
Type I hypersensitivity is primarily due to…
Anaphylactic hypersensitivity due to allergies.
What are the key components of Type I hypersensitivity reactions?
IgE, Mast cells, Basophils, Eosinophils.
What are the clinical manifestations of Type I hypersensitivity reactions?
Allergic rhinitis, allergic asthma, food allergies, skin reactions, anaphylaxis.
What are the primary methods of testing for Type I hypersensitivity?
Skin testing - percutaneous or intradermal.
What is a positive result for Type I hypersensitivity skin testing?
Wheal and flare at the site of application; diameter >3-4 mm is a positive result for that particular allergen.
What are other testing methods are used for Type I hypersensitivity?
Allergen specific IgE testing, total IgE testing.
Type II hypersensitivity is classified as antibody-mediated ___.
cytotoxic hypersensitivity.
Which immunoglobulins are directed against cell surface antigens in Type II hypersensitivity?
IgG and IgM.
What effects does Type II hypersensitivity have on antibodies?
Cell destruction; inhibition of cell function; increase in cell function.
What are clinical examples of Type II hypersensitivity?
Transfusion reaction; hemolytic disease of the newborn; autoimmune hemolytic anemia; Goodpasture’s syndrome; Hashimoto’s disease.
Define Goodpasture’s syndrome.
A Type II hypersensitivity disorder that involves antibodies attacking tissues, specifically the kidneys and lungs.
What laboratory methods are used in Type II hypersensitivity testing?
Direct Antiglobulin Test (DAT) and Indirect Antiglobulin Test (Coombs test).
What occurs with a positive DAT test?
Agglutination.
The Coombs test tests patient serum for what?
Antibodies to RBC antigens.
Type III hypersensitivity is classified as…
Complex-mediated hypersensitivity.
In Type III hypersensitivity, what precipitates out and deposits into tissues?
Antigen-antibody complexes.
In Type III hypersensitivity, complement binds causing ___ and ___ to increase.
vasodilation; vasopermeability.
In Type III hypersensitivity, ___ and ___ migrate and release lysosomal enzymes which cause tissue damage.
macrophages; neutrophils.
Describe the Arthus reaction in Type III hypersensitivity.
A skin reaction with localized inflammation with redness and edema that peaks around 3-8 hours.
Describe serum sickness in Type III hypersensitivity.
Passive immunization of humans with animal serum. Antibodies are produced against the foreign animal proteins and immune complexes are deposited into tissues.
What are the laboratory testing methods used for Type III hypersensitivity?
ANA testing; fluorescence staining of tissue sections to detect immune complexes; testing for RF; testing complement levels.
In Type III hypersensitivity, a decreased complement level in serum is indicative to what?
High disease activity.
Type IV hypersensitivity is classified as what?
Cell-mediated hypersensitivity.
What types of cells are involved in Type IV hypersensitivity?
Th1 cells and macrophages.
In Type IV hypersensitivity, Th1 cells release ___ that attract and activate macrophages.
cytokines.
In Type IV hypersensitivity, macrophages induce ___.
inflammation.
Type IV hypersensitivity peaks ___-___ hours after antigen exposure.
48-72.
What are the clinical manifestations for Type IV hypersensitivity?
Contact dermatitis; hypersensitivity pneumonitis; infections with intracellular pathogens.
