Exam 3: Dr. Pharr Hypersensitivity Flashcards
What is hypersensitivity?
Exaggerated immune responses that cause inflammation and tissue damage
What are the 4 types of hypersensitivity reactions and their effector mechanisms?
Type I: IgE-mediated hypersensitivity to harmless antigens
Type II: Antibody-mediated destruction of cells
Type III: Immune complex mediated
Type IV: T-cell mediated
What is a type I hypersensitivity reaction?
Allergic response to harmless environmental antigen
What is an allergy?
A state of hypersensitivity to a non-harmful antigen
What is sensitization of type I hypersensitivity reactions?
Initial exposure generates a primary immune response
When do germinal centers form?
In the second week of the primary response
What do germinal centers do?
Isotype switching to IgE
Memory B cells and long-lived plasma cells
Mast cells express the high-affinity Fc receptor for IgE and therefore bind free IgE from the blood
When does the early phase of type I hypersensitivity reactions local response occur?
Immediately
What is the effector function of IgE?
Activation of mast cells, which degranulate and release histamine and TNF-α
When does the late phase of type I hypersensitivity reactions local response occur?
After 6-8 hours
What is involved in mast cell synthesis?
Prostaglandins and leukotrienes came vasodilation and vascular permeability
Cytokines and chemokines recruit leukocytes
Describe the emigration of eosinophils in response to mast cell-derived chemokines in type I hypersensitivity reactions
Respond to mast cell-derived cytokines
Release tissue damaging proteases
Describe the emigration of basophils in response to mast cell-derived chemokines in type I hypersensitivity reactions
IgE mediated activation or respond to mast cell-derived cytokines
Release histamine
What does the emigration of leukocytes in response to mast cell-derived chemokines in type I hypersensitivity reactions result in?
Narrowing of the airway or sustained edema
What is the systemic response of type I hypersensitivity reactions?
Allergen enters the bloodstream:
IgE-mediated activation of mast cells
What is anaphylaxis?
An immediate type I hypersensitivity reaction causing circulatory shock and suffocation due to bronchiole constriction
What does histamine release by mast cells do?
Vasodilation and vascular permeability – decreases blood pressure
Bronchial smooth muscle contraction
Intestinal smooth muscle contraction
What are examples of allergens?
Drugs
Insect venoms
Foods
What is the sensitization of type II hypersensitivity reactions?
Some drugs can bind to self protein and induce a primary immune response i allergic individuals
What is a classic examples of type II hypersensitivity reactions?
Antibiotics such as penicillin
Describe drug-induced hemolytic anemia
Drug binds to delf proteins to generate new epitope
Activation of a primary response to a new epitope
Germinal center formation results high affinity
What could future exposure of the drug in type II hypersensitivity reactions cause?
Antibiotics bind to self proteins
Drug-induced IgG binds to the surface of RBCs
What is drug-induce hemolytic anemia?
RBCs are opsonized by IgG and activated complement C3b. This results in the removal of opsonized erythrocytes by macrophages in the spleen
What is the local response of type III hypersensitivity reactions?
Artus reactions–immune complexes form in the tissue, cause localized inflammation
What is a classic example of type III hypersensitivity local response reactions?
Booster vaccination sometimes results in swelling and/or pain at the injection site
Residual antibodies from previous vaccination form immune complexes with the vaccine antigen
What is an immune complex?
Antibody with its antigen
What will immune complexes in type III hypersensitivity reactions do?
Activate the classical pathway of complement
Describe complement activation in type III hypersensitivity reactions
Proinflammatory
Mast cells will degranulate in response C5a and signals through the Fc receptor for IgG
What is the systemic response of type IIII hypersensitivity reactions?
Serum sickness–immune complexes form n the bloodstream
Immune complexes can form in the capillaries of a number of tissues and induce inflammation
What is a classic examples of a systemic response to type III hypersensitivity reactions?
Treatment for snake bites. Antiserum from horses immunized with snake venoms
What can the antiserum from horses occur with?
Injection of a large amount of poorly catabolized foreign antigen (horse IgG)
When does the immune response to horse IgG occur?
Within 7-10 days
What is the sensitization phase of the delayed-tpye hypersensitivity in type IV hypersensitivity reactions?
Primary immune response
What is the elicitation phase of the delayed-tpye hypersensitivity in type IV hypersensitivity reactions?
Mediated by memory Th1 helper T cells
What is the classic example of delayed type hypersensitivity of type IV hypersensitivity reactions?
Tuberculin skin test
Requires previous infection with Mycobacterium tuberculosis or vaccination with the BCG
What are other test for cel-mediated immunity in type IV hypersensitivity reactions?
Anthraxin test
Candidin test
What is anthraxin test?
Bacillus anthracis
Cell wall preparation from the attenuated strain
What is the candidin test?
Yeast extract from Candida albicans
What are type IV hypersensitivity reactions due to?
Intracellular pathogens
Is a delayed-type hypersensitivity of a type IV hypersensitivity reaction duet an allergy?
No
What is a contact hypersensitivity of a type IV hypersensitivity reaction?
Allergic response to chemically modified self proteins
What is a classic example of contact hypersensitivity of type IV hypersensitivity reactions?
Poison ivy
Chemical from the leaf, pentadecacatechol, is lipid soluble
The chemical can form covalent bonds and modify extracellular skin proteins (presented by MHC class II) or enter a cell and modify intracellular proteins (presented by MHC classI)
What happens with allergic contact dermatitis in type IV hypersensitivity reactions?
Activation of memory Th1 helper T cells; pro-inflammatory cytokines
Activation of memory CTL; cellular cytotoxicity and IFN-γ
What are the 2 types of contact dermatitis?
Allergic contact dermatitis
Irritant contant dermatitis
What is allergic contact dermatitis?
Immunological form
Allergic response to an antigen
What is irritant contact dermatitis?
Non-immunological form
Response to chemical to irritate or traumatize the skin
No sensitization
Can occur immediately
What is a mechanism for irritant contact dermatitis?
A wide range of chemicals can activate keratinocytes to produce pro-inflammatory cytokines and chemokines
