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Describe cells involved in antigen exposure and generation of IgE in type I allergic response.
APCs (HLA class II) present processed peptides to helper T-cells, releasing interleukins (IL-4, IL-13) which transform B-cells to plasma cells that generate IgE.
What is the primary reaction phase in an IgE mediated (type I) allergic response.
- Sneezing, rhinorrhea, congestion, nasal pruritus
- Occurs in minutes (max effect in 15 min)
- IgE attaches to mast cells and basophils
- release of preformed mediators (histamine, seratonin, proteases) and newly generated mediators (TNF-alpha and arachadonic acid derivatives - leukotrienes, prostaglandins)
What is the secondary (late) phase of an IgE mediated allergic response?
- 4-6 hours after exposure
- peristent congestion, rhinorrhea, sneezing
- migration of neutrophils and eosinophilsmast cells inactive, basophil releases mediators
Describe a type I hypersensitivity (type, meditors, reactions)
- Anaphylactic, IgE mediated response
- stimulates mast cells and basophils to release histamine and other mediators
Describe a type II hypersensitivity (type, meditors, reactions)
- Cytotoxic (against self)
- IgG, IgM binding to phagocyte or complement
- eg: transfusion rxn, goodpastures
Describe a type III hypersensitivity (type, meditors, reactions)
- Immune complex
- IgG, IgM, IgA complexes increase blood viscosity
- removed by reticuloendothelial system
- eg: glomerulonephritis, serum sickness
Describe a type IV hypersensitivity (type, meditors, reactions)
- T-cell mediated, delayed
- eg: graft rejection, contact dermatitis
What percentage of allergic rhinitis patients have asthma?
- 1/3 (33%)
- both involve mast cells and eosinophils in pathophysiology
- nasal-bronchial reflex: nasal histamine provocation increases lower airway resistence
Common allergens by season
- Trees and grass (spring/summer)
- ragweed, tumbleweed (fall)
- dust mites (may increase in winter due to closed windows)
- molds (perennial, may worsen when damp/humid)
Describe skin prick testing. What are its advantages?
- allergen placed on skin, followed by prick through droplet into skin
- most convenient, least expensive method
- must avoid antihistamines 72 hours priorrisk of anaphylaxis, not as sensitive as RAST, subjective
What is an "intradermal test", how does it compare to skin prick test?
- Intradermal bleb introduced with 26 or 27 ga needle.
- more sensitive
- greater risk of anaphylaxis
Describe radioallergosorbant testing. What are its advantages of skin-prick testing?
- react serum with series of known allergens
- labelled anti-IgE identifies antigen-IgE complexes
- highly specific (less sensitive)
- no conflict with meds (antihistamines, B blockers)
- no risk of anaphylaxis
- disadv: expensive, takes weeks for results, less sensitive
indications for RAST testing
- high risk of anaphylaxis
- skin disorders
- uncooperative patient
- equivocal skin test (negative skin test NOT an indication)
- failed immunotherapy
How do beta blockers relate to allergy?
increase sensitivity to allergens
indications for immunotherapy?
- severe persistent symptoms
- unavoidable allergens
- failed maximal medical management
- wish to avoid chronic medication
- coexisting asthma (that is not severe or unstable)