(L28) Hypersensitivity Flashcards
What are the characteristics of type I hypersensitivity?
Timing and mechanism.
L28 S4
Immediate response
Caused by degranulation of mast cells and eosinophils stimulated by IgE
Induced by Th2 responses/IL-4
What are the mast cell mediators involved in Type I hypersensitivities?
L28 S5
Histamine:
-vasodilator and increased permeability
Protease:
-tissue damage
Prostaglandins
-vasodilator
Leukotrienes:
-smooth muscle contraction
Cytokines:
-inflammation/leukocyte recruitment
What is unique to first and subsequent exposures in type I hypersensitivities?
L28 S6-7
First exposure to allergen:
- causes B cell maturation and production of plasma cells that produce IgE
- no hypersensitivity response as allergen is likely gone before IgE is produced
Subsequent exposures to allergen:
- circulating IgE bind allergen and bind to FcεRII (CD23)
- degranulation occurs due to cross-linking of FcεRII
What are the different phases of a type I hypersensitivity response?
L28 S9
Immediate phase:
- occurs within minutes
- due to degranulation
- vasodilation, congestion, and edema
Late phase:
- occurs 2-24 hours later
- due to leukocyte infiltration
What is allergen-SIT?
L28 S13-14
Administration of allergen in increasing doses to cure allergies
Functions:
- induces T cell tolerance (Tregs)
- increases threshold for degranulation
- decreased IgE-mediated histamine release
What are the characteristics of type II hypersensitivity?
L28 S16
IgG/IgM interaction with cell/tissue SURFACE Ags
Classical complement activation and production of anaphylatoxins resulting in leukocyte recruitment
Opsonization of cell via IgG causing neutrophil and macrophage activation
What are examples of type II hypersensitivity that don’t results in cell damage but instead have other physiological responses?
L28 S18
Grave’s disease:
- binding of Ab to TSH receptor in thyroid, activating them
- results in hyperthyroidism
Myasthenia gravis:
-binding of Ab to ACh receptor in neuromuscular synapses blocking stimulation
What are examples of type II hypersensitivity?
L28 S23
- hemolytic anemia (Rh and I antigen)
- thrombocytopenia purpora (platelet cells)
- Goodpasture’s syndrome (basement membrane of glomeruli
- Grave’s disease
- myasthenia gravis
- Pemphigus vulagaris (desmosomes)
- rheumatic fever (cross reaction with myocardial antigens following streptococcal infection)
What are the characteristics of type IV hypersensitivity?
Timing and mechanism.
L28 S27
Delay-type hypersensitivity (DTH) (24-48 hours)
Caused by reaction of of T cells to Ag
CD8+ mediated cell killing
CD4+ (Th1/17) and macrophage cytokine mediated inflammation leading to cell damage
What are the characteristics of type III hypersensitivity?
L28 S24
IgG/IgM interaction with cell/tissue SOLUBLE Ags
Formation of immune complexes which deposit in vessels causing complement activation and leukocyte recruitment/activation
Especially problematic in lungs and kidneys
Results in ischemia
What are examples of type III hypersensitivity?
L28 S25
- systemic lupus erythematosus (DNA)
- polyarteritis nodosa
- post-streptococcal glomerulonephritis
- serum sickness (systemic vasculitis)
- Arthus reaction (local vasculitis)
What is the mechanism of reaction to poison ivy?
L28 S31
Pentadecacatechol from poison Ivy complexes with skin protein forming a neoantigen.
The pentadecacatechol is too small to form an immune reaction on its own (hapten)
What are examples of type IV hypersensitivity?
L28 S29
- multiple sclerosis (myelin)
- rheumatoid arthritis
- Type 1 DM (pancreatic β cell Ags)
- Crohn’s disease
- contact sensitivity (poison ivy haptens)
- chronic infections (ie. tuberculosis)
What are examples of type I hypersensitivity?
L28 S4;10–11
Anaphylaxis (systemic) Asthma (local) Acute urticaria (bug bites) Allergic rhinitis (pollen) Food allergies
What are the most common contact allergens?
L28 S32
Metals:
- nickel
- cobalt
- chromium
