Lec14Food Allergy Flashcards
What are some things often confused with allergies?
toxic/pharmacologic causes
- bacterial food poisoning
- scromboid fish poisoning
- caffeine
intolerance: lactase deficiency
What is the pathogenesis of food allergy
Ingest food into gut, instead of getting Treg stimulation to produce regulatory cytokines [TGF-B, IL-10] —> either IgE or non IgE mediated response
- TH2 cells generated and direct IgE antibodies
- —- IgE antibodies specific to epitope on food protein bind mast cells [that have high affinity IgE receptors] and mast cells
- —- Re-expsorue causes IgE cross linking –> mediators [ie histamine] released
- —- IgE mediated response
- OR T cells produce cytokines that cause allergic [eosinophilic] inflammation [IL-5]
- —- non-IgE mediated response
What is IgG response in gut?
- when soluble proteins pass through barriers [glycocalyx, epithelial cells, etc] they are processed in lamina propria
What is IgA response in gut?
When viruses or bacteria processed by M cells overlying Peyer’s patches
What allergy reactions traditionally IgE mediated?
- urticaria angioedema
- ashtma
- rhinitis
- GI anaphylaxis
- oral allergy
- system anaphylaxis or food associated/exercise induced anaphylaxis
What allergy rxns traditionally non-IgE mediated
- enterocolitis
- enteropathy
- celiac
What allergies mixed?
- eosinophilic esophagus
- atopic dermatitis
Symptoms of allergy
- hives, sweeling itchy
- vomit, diarrhea, pain, mouth symptoms
- altered consciousness, poor pulse, low BP
- throat closing, coughing, hoarse wheeze
Are IgE or non IgE faster rxn
IgE
Prick skin test
- rapid, sensitive test to detect specific IgE
- get wheal [bump] and flare [surrounding red]
- histamine = positive control [makes blood vessels leaky]
- salt water = negative control
- must be off antihistamines
- positive test does not prove symptomatic sensitivity just suggests likelihood
Serum Food-Specific IgE “RAST” Test
- blood test to measure specific IgE
- put protein of interest on matrix
- add patient serum
- wash
- used secondary anti-IgE labeled antibody with marker
- Measure fluoresence to see amount of IgE specific to protein [ex. almond]
- less sensitive than prick skin test
- not affected by antihistamine use
- report level, class, percent of antibodies
- if nevative means there is no IgE mediated allergy
- if positive still not proof of symptomatic allergy
Why do some people with IgE positive RAST or skin test have no allergic symptoms? What factors involved
- if cell mediated: may get positive skin but negative IgE test
- Different amount of Ig: more Ig = more likely to have symptoms to allergy
- Different affinity: if lower affinity Ig may not stick well to almond, don’t get symptoms
- Different binding pattern: Ig that binds one part of protein may have bigger effect than Ig that binds another part
- binds to protein that breaks down easily: then antibody might not really have time to see and interact with the antigen
How does digestion of protein antigen [ex peanut] affect allergic response?
- antibody might bind to an epitope in its normal conformation
- when antigen digested –> if epitope destroyed then antibody may no longer be able to bind properly
oral food challenge
- food eaten gradually in increasing amount with physician supervising and emergency treatment on hand
- open, single-blind, or double-blind/placebo controlled challenge
- allows you to verify allergy/tolerance AND diagnose non-IgE mediated food allergy
Oral allergy syndrome [pollen-food syndrome]
- oral syndrome of mouth itch
- related to pollen allergy
- usually no symptoms beyond mouth
- cooking destroys protein
- – do commercial skin test [cooked] vs fresh skin test
- may be concentrated in peel
- birch allergy: apple, plum, cherry, apricot
- ragweed allergy: watermelon, melon
- type of IgE mediated
