l18 Flashcards
what is skin prick testing
Detection of allergen-specific IgE in vivo:
Allergen extract applied as drops
Top layers of epidermis punctured with lancet
A wheal with flare response after 15 minutes is positive
Result needs interpretation in clinical context
how to detect for an allergen-specific IGE in vitro using an elisa
- Plastics coated with purified allergen of interest. Incubate with patient serum
- IgE antibodies in sera of sensitised patient bind to allergens
- Immobilised IgE antibodies detected with polyclonal anti-IgE detection antibody
what is the action of Nasal decongestants
eg oxymetazoline
Act on α1 adrenoreceptors to cause vasoconstriction
Only for short-term use
Topical and systemic
what is the action of B2 agonists
Eg salbutamol
Act on lung B2 adrenoreceptors, cause smooth muscle relaxation
what is the action of Epinephrine
Systemic adrenergic effects oppose vasodilatation and bronchoconstriction
give 2 classes of drug that treats early-phase mediators
1-H1 Antihistamines
2-Leukotriene receptor antagonists
give the name action and characteristics of a mast cell stabiliser
sodium cromoglycate
Reduce mast cell degranulation by unknown mechanism
Not orally absorbed – topical use only
Short half-life requires frequent dosing
Main benefit is steroid-free, but efficacy very poor
what is a first and 2nd generation H1 antihistamine
1st generation eg chlorpheniramine
Considerable sedation, drug interactions
2nd generation eg cerizine, loratidine, desloratidine, fexofenadine
No/ minimal sedation, once-daily
give an example of a leukotriene receptor antagonist
Only UK drug is Montelukast
Effective in reducing early allergic responses, but inferior to H1 antihistamines
Unlike anti-histamines, beneficial in chronic asthma, which is the main indication for their use
what types of cells do corticosteroids work on
Steroids reduce immune activation by altering gene expression in numerous cell types, including T cells, B cells and cells of the innate immune system. Their onset of action is delayed and they must be taken regularly
what is in the brown asthma inhaler
Inhaled
Eg beclamathosome, fluticasone
what can be used to treat seasonal rhinitis
Nasal
Eg beclamathasone, mometasone, fluticasone
what are the side effects of corticosteroids used orally, via nose, and topically
oral candida
nose bleeds
local skin thinning
what is omalizumab
is a monoclonal antibody directed against IgE, used for atopic asthma (amongst other things)
it binds to free IGE decreasing cell-bound IGE (binds to Fc region)
decreses the expression of high-affinity receptors
decreases mediator release
decreases allergic inflammation & prevents excacerbation of asthma and reduces symptoms
what is allergen specific immunotherapy
Allergen doses administered by subcutaneous injection or sublingually
Provide long-term protection
Mainly venom allergy and rhinitis
Multiple immunological effects:
Induce regulatory T cell responses to allergens
Reduce Th2 responses
Induce allergen-specific IgG antibodies
Reduction in mast cell responsiveness
Reduce allergen-specific IgE levels
what is contact dermatitis
Sensitising agents are typically highly reactive small molecules which can penetrate skin
These react with self proteins to create protein-hapten* complexes that are picked up by Langerhans cells, which migrate to regional lymph nodes
The Langerhans cells process and present the antigen together with MHCII
In some susceptible individuals, the complexes are recognised as foreign
The activated T cells then migrate to the dermis
what is haptenisation
*Hapten=small molecule which cannot produce an immune response by itself, but can bind to a protein to alter its immunogenicity
what is the elicitation process of contact dermatitis
Chemokines recruit macrophages
Th1 cells secrete IFN gamma: increases expression of vascular adhesion molecules, activates macrophages
TNF alpha/ beta: local inflammation
what is the hallmarker of Th1 T cells
TNF-gamma
how does poison ivy irritate the skin
Pentadecacatechol is a poison ivy lipid that may cross the skin and modify intracellular proteins
These proteins are processed and presented with MHC1 to CD8 T cells which then cause contact dermatitis
Again, not everybody is susceptible
Historical reports suggest that native Americans would feed their babies poison ivy to generate tolerance
what is patch testing
Antigen-impregnated patch placed on back
Nickel, chrome, cobalt, epoxy resin, lanolin etc
Results read after 2 days
what is the difference between contact dermatitis and type 1 allergy
Clinical features-
Various features consistent with mast cell degranulation-
Eczematous skin reaction
Temporal aspects-
Closely follows exposure then improves fairly rapidly-
Delay between exposure and symptoms
Causative agent-
Almost always naturally-occurring protein or closely related to one-
Various, often synthetic molecules
Effector mechanism-
Allergen-specific IgE, mast cell degranulation-
Antigen-specific effector
Th1 cells
Assessment-
Allergy clinic – history, skin prick testing, serology for allergen-specific IgE-
Dermatology clinic (UK) or Allergy clinic (Europe), history and patch testing
Management-
Avoidance if possible, pharmacotherapy, immunotherapy-
Avoidance only
what is the difference between skin prick testing and patch testing
Indication-
History suggestive of IgE-mediated allergy-
History suggestive of contact dermatitis
Test format-
Allergen extract drops applied to skin, skin punctured, read after 15 minutes-
Test antigen applied under occlusive dressing, read after 48 hours
Positive-
Wheal and flare response-
Eczematous reaction
describe the Tuberculin skint test (TST) and what type of allergy is it
type 4
Used to determine EXPOSURE to TB
Chemoprophylaxis may be indicated to reduce risk of reactivation
Tuberculin injected intradermally (tuberculin=complex mixture of antigens derived from MTB)
Local inflammatory response evolves over 24-72 hours if previously exposed
Fairly poor test for active TB
