Hypersensitivity Flashcards
T or F: Hypersensitivity is an innate immune response that is inappropriate or exaggerated.
- false!
- hypersensitivity is an ADAPTIVE immune response that is inappropriate or exaggerated
What are the four types of Hypersensitivity? Which ones are antibody mediated? T-cell mediated?
- type I: antibody mediated (IgE); allergy
- type II: antibody mediated (IgG); antibody-dependent cytotoxicity
- type III: antibody mediated (IgG); immune complex deposition
- type IV: T-cell mediated; “delayed-type”
Allergens favor a (TH1/TH2) response, resulting in a (CELL-MEDIATED/HUMORAL) response.
- (type I HS)
- allergens favor a TH2 response
- results in a humoral response (B cells with IgE)
T or F: Mast cells are circulating cells with high-affinity IgE receptors.
- false!
- mast cells are tissue-based (not circulating) with high-affinity IgE receptors (FcERI)
What are the two phases of an allergic (type I HS) response?
- 1) sensitization (1st exposure)
- 2) elicitation (subsequent exposure)
What triggers mast cell degranulation in the context of a type I HS?
- cross-linking of mast cell bound IgE (requires the allergen)
In an allergic reaction (type I HS), what causes the immediate response? What causes the late-phase response?
- immediate: caused by the degranulation of mast cells and the resulting release of histamine and LTs triggering inflammation w/ bronchoconstriction and mucus secretion
- late-phase: caused by the immune response triggered by histamine and LTs; eosinophils, neutrophils, etc. (occurs about 6 hours later)
Type II Hypersensitivity
- antibody-dependent cytotoxic HS
- IgG related
- cells are marked by antibodies and killed by NK cells and cytotoxic T-cells (CD8+ cells)
Examples of Type II Hypersensitivity
- reactions against blood cells and platelets, grave’s disease, myasthenia gravis
- hyperacute graft rejection
Which type of HS reaction is responsible in hyperacute graft rejection? In chronic rejection?
- hyperacute: type II
- chronic: type IV
Autoimmune Hemolytic Anemia is a Type ___ Hypersensitivity reaction in response to ___________.
- (autoimmune hemolytic anemia is when we destroy our own RBCs)
- type II HS
- can be caused by exposure to Penicillin
Type III Hypersensitivity
- immune-complex deposition in blood vessels and tissues cause damage and impede function
Why doesn’t the build-up of immune-complexes (as seen in Type III HS) occur in normal circumstances?
- because RBCs have CR1 receptors that bind to immune complexes and bring them to the liver and spleen for removal
- the deposition occurs when the rate of IC formation exceeds that of RBC clearance (this is what happens in type III HS)
Serum Sickness
- an example of type III HS
- foreign serum proteins are introduced into the body, resulting in prolonged Ab production –> IC formation exceeds RBC clearance = deposition
Type IV Hypersensitivity
- delayed-type HS; mediated by T-cells and macrophages (Ab independent)
What are the “Four T’s” of Type IV HS?
- T-cells, tuberculosis (when testing for TB), transplant (rejection), and touching (contact dermatitis)
Contact Dermatitis
- an example of a type IV HS
- results from an initial and subsequent exposure to an allergen coming into direct contact of the skin
- (nickel, poison ivy, soaps)
Contact Dermatitis is an allergic reaction, involving a sensitization and elicitation phase, so why isn’t it classified as a Type I HS?
- it is type IV and not type I because it only involves a cell-mediated immune response (antibodies are NOT involved)
