Exam 4 Lecture 20: Allergies, Asthma, Hypersensitivity Flashcards
What are the major components of a Th2 response?
Antibodies: IgE bound
Innate effector cells: Mast cells (long lived, tissue resident) Basophils (short lived, circulatory) Eosinophils (short lived, tissue resident)
T cells: Th2 CD4+
What is the allergy loop
Th2 CD4 T cells influence B cells to class switch to IgE
What are the 4 Types of Hypersensitivity Reactions and what immune mechanisms mediate each type?
Type I: IgE-mediated (traditional allergies)
Type II: IgG-mediated
Type III: Immune complex-mediated
Type IV: T cell-mediated
What is the relative timing of each of the 4 types?
Type I: Within 1 hour
Type II: Hours to days
Type III: 1-3 weeks
Type IV: Days to weeks
What are some examples of each of the 4 types?
Type I: nut allergy, bee sting, pollen
Type II: RhD mismatch
Type III: serum sickness, SLE
Type IV: TB skin test, poison ivy, nickel
Type 1 hypersensitvity
Triggered by allergen specific IgE on mast cells, basophils, eosinophils
Leads to degranulation, immediate response
Cannot occur at first exposure (allergen specific IgE is developed at firs exposure)
Three types of Type 1 reactions
- Anaphylaxis: systemic
immediate results following allergen exposure
sudden shock syndrome resulting from the massive
systemic release of mast cell mediators
death can occur within 30 mins - Allergic rhinitis/asthma: nasal/respiratory
caused by inhalation of allergens
can turn into chronic asthma - Urticaria: skin
activates mast cells in the skin, causes hives
How is Type I Hypersensitivity diagnosed through skin tests and blood tests?
Skin test: A small amount of possible allergen is put under the skin, positive test will be a small red bump
Histamine as positive control, saline as negative
Problems: skin will react differently than gut
Blood test: Serum IgE measured by ELISA test
allergen extract is added to well, sample on top, then an antibody
Problems: must have had at least one exposure, IgE doesn’t stay on blood very long
Type 2 Hypersensitivity
IgG response to modified cell surface: induce complement cascade and antibody dependent cellular cytotoxicity (ADCC)
Often a foreign blood antigen (ex. RhD)
Type 3 Hypersensitivity
Immune complex mediated (IgG bound to antigen)
Cause local inflammation and are eventually deposited in the kidney and liver, where they
cause pathology
Serum sickness
Often generated following exposure to proteins derived from animals, often found in sera or antitoxin
Can take up to 2 weeks for symptoms to appear:
* rashes and itchy skin
* fever and joint pain
* glomerulonephritis
* swollen lymph nodes
Treated with corticosteroids and antihistamines
Type 4 Hypersensitivity
T cell mediated, aka DTH delayed type hypersensitivity
Sensitivity and effector phases
Reaction does not happen immediately during the first exposure, because it requires T cell priming
When are Type IV Hypersensitivity reactions used as diagnostic tests?
A foreign antigen is injected to test whether there are signs of an effector phase.
Example: Skin test for bovine tuberculosis
How are Type IV Hypersensitivity reactions diagnosed through a Patch Test?
Day 1: Several strips are applied to the back, each strip contains small aluminum disks containing a different substance
Day 3 (48 hours): Disks are removed, the skin is examined for reactions such as redness, inflammation, swelling
Day 5 (96 hours): After about 96 hours, the patches are
examined again for evidence of reaction
What are treatments for allergies involving behavior changes, drugs, or immunotherapy?
