Toni and Dave Hutchinson Flashcards
Definition of allergy
a hypersensitivity reaction initiated by immunologic
mechanisms (Antibody- or Cell-mediated). In the majority of
cases allergy is IgE-mediated.
Definition of hypersensitivity?
causes objectively reproducible symptoms or
signs , initiated by exposure to a defined stimulus that is
tolerated by normal subjects.
Definition of atopy
genetic predisposition to become sensitized and
produce IgE antibodies on exposure to common
environmental allergens
Examples of nnon allergic food hypersensitivity?
- Toxic/Pharmacologic (Bacterial poisoning, etc)
- Non-toxic / Intolerance (Lactase deficiency, etc)
Examples of IgE mediated food allergy?
- Urticaria - Angioedema
- Anaphylaxis
- Oral Allergy Syndrome
- Immediate gastrointestinal allergy
- Atopic dermatitis
- Asthma - Rhinitis
Examples of non IgE mediated food allergy
- Protein-Induced Enterocolitis/proctocolitis
- Celiac disease
- Dermatitis herpetiformis
- Food-induced Pulmonary Hemosiderosis
Immunotherapy for allergic asthma?
Omalizumab - monoclonal IgE antibody
Diagnostic pathway for allergies?
- History
- Physical examination - e.g. wheezing, urticaria, increase HR etc.
- Allergy tests
- Skin prick (Prick, intradermal, APT)
- Blood test for IgE (RAST, CAP)
- Challenges (Open, DBPCFC)
- Other (BHR, epitopes)
What do we need to know about a food allergy?
When and where ? (age of patient, environment)
What food ? (ingredients, preparation, quantity)
What symptoms ? (timing, onset, duration, reproducibility)
What associated factors ? (exercise, drugs)
What treatment ? (medication, response)
What management plan ? (avoidance, re-exposure)
What does the IgE (CAP/RAST) test check?
Multiple allergens against patients serum
When should you consider serum specific IgE test?
- Skin disorder (dermagraphism)
- Unable to discontinue medication (antihistamines)
- Suggestive history
When can you not do skin prick test
When you are on antihistamines
What is considered a positive value in the IgE serum test?
Results expressed in kUa/L (positive > 0.35 kUa/L)
What is the gold standard for challenge testing?
double-blind placebo-controlled challenges (DBPCC)
Natural history of food allergis?
80-90% outgrown by age 5
What is Hymenoptera venom allergy
bumble bee sting
What is Hymenoptera venom allergy
bumble bee sting
Relevance of investigations for allergies (BMJ)
- Serum tryptase
- More specific to mast cells
- Usually undetectable in healthy individuals
- Not useful in food-induced anaphylaxis with local reaction - In vitro IgE testing
Putting known allergen in with patient’s serum IgE
- Tagging other IgE molecules with immunofluorescence to see if they have bound - Skin test
- >3mm diameter and greater than control
- Low diagnostic value for food allergy testing
- If negative do the challenge test - Challenge test
- Expose patient to increasing amount of offending allergen
Relationship between NSAIDs and allergic reactions?
Regardless of COX selectivity pattern, NSAIDs may function as haptens capable of inducing allergic sensitization. Unlike anaphylaxis, anaphylactoid reactions are most likely related to inhibition of COX-l by NSAIDS. Thus, an anaphylactoid reaction caused by a particular COX-1 inhibiting NSAID will occur with a chemically unrelated NSAID which also inhibits COX-1 enzymes. Selective COX-2 inhibitors appear to be safe in patients with a history of NSAID-related anaphylactoid reactions but can function as haptens, with resulting sensitization and anaphylaxis upon next exposure.
NSAIDs may also trigger cell activation by altering arachidonic acid metabolism. Activation of complement, the complement peptides (anaphylatoxins) such as C3a and C5a, and their direct action on mast cells and basophils may lead to mediator release, producing symptoms indistinguishable from the classic IgE-mediated reaction
Outline the process of sensitisation in anaphylaxis
Sensitisation:
Allergens carried to LNDs by APC’s and present allergen to T helper cells
Expression of costimulatory molecules
Differentiates into Th2 cell via IL4, 5, 10
Th2 release IL4 causing class switching of B cells to IgE
IL5 release = eosinophils
IgE attach to Fc receptors on mast cells AND BASOPHILS
Outline the process of cross-linking in anaphylaxis
2nd exposure to antigen crosslinks IgE
Activation of mast cells
Histamine, prostaglandin D2, leukotrienes, platelet-activating factor, tryptase, nitric oxide, and eosinophil and neutrophil chemotactic factors have diverse effects on target organs and lead to the clinical manifestations of anaphylaxis.
Outline the early phase reaction in anaphylaxis
Vasodilation
Urticaria (hives)
Edemia
Bronchoconstriction
Outline the late/delayed phase reaction in anaphylaxis
Occurs due to release of arachadonic acid metabolites e.g. leukotrines
IL4, 5, 10 and leukotrienes (LTB4 and LTC4)
Damage to epithelium
Attraction of more immune cells