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204 theme 1 > 17. atopy, allergy and delayed type hypersensitivity > Flashcards

17. atopy, allergy and delayed type hypersensitivity Flashcards

1
Q

allergen definition

A

substance to which IgE antibodies may be produced

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2
Q

early phase allergic reaction

A

in allergic individuals, allergen exposure lead to rapid development of symptoms (seconds-minutes)
allergens bind to IgE antibodies on mast cells and basophils

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3
Q

IgE ligation in allergy

A

IgE binds specific allergen
cross-linking of IgE by allergen beads to clustering of receptors
intracellular portion of receptor becomes phosphorylates
intracellular cascade leads to cell activation
mast cells degranulate - release histamine, tryptase and other preformed mediators

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4
Q

leukotrienes

A

delayed mediators
similar pharmacological effect to histamine
phospholipase A2 from mast cell activation starts pathway
derived from arachidonic acid

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5
Q

pharmacological effects of mast cell mediators and leukotrienes

A

skin - wheal and flare
nose - discharge, sneezing
eyes - conjunctivitis
lungs - wheeze

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6
Q

mast cell activation and granule release - GI tract

A

increased fluid secretion
increased peristalsis
expulsion on gastrointestinal tract contents (diarrhoea, vomiting)

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7
Q

mast cell activation and granule release - airways

A

decreased diameter
increased mucus secretion
congestion and blockage of airways (wheezing, coughing, phlegm)
swelling and mucus secretion in nasal passages

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8
Q

mast cell activation and granule release - blood vessels

A

increased blood flow
increased permeability
increased fluid in tissues - increased flow of lymph to lymph nodes, increased cells and protein in tissues
increased effector response in tissues

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9
Q

allergen sources

A

almost always otherwise innocuous environmental proteins

pollen, house dust mite faeces, stinging insect venom

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10
Q

general characteristics of allergens

A

proteins (minor exceptions) - only protein can produce T/B cell response
physical properties favour transition across mucus membrane (soluble, low molecular weight)
biologically active (often enzymes)
moderate homology with self-proteins

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11
Q

clinical allergy syndromes: anaphylaxis

A

generalised allergic reaction
systemic release of histamine
causes generalised vasodilation and fluid loss from circulation into tissues
foods, drugs and insect venom = most common in UK

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12
Q

anaphylaxis symptoms

A

hives, angioedema
vomiting, diarrhoea, laryngeal oedema, bronchoconstriction
vasodilatation, hypotension

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13
Q

anaphylaxis cardinal features

A

typical symptoms
multi-system and dramatic
rapidly follows exposure to allergen
tends to improve quickly thereafter

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14
Q

clinical allergy syndromes: oral allergy syndrome

A

most common type of food allergy in the UK
IgE against pollen proteins cross-reacts with homologous proteins in plant-derived food
oral itching on exposure to raw fruit, nuts and vegetables
UK - pollen mainly birch, food mainly Rosaceae fruits

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15
Q

clinical allergy syndromes: airway disease

A

rhinitis - sneezing, rhinorrhoea, blockage (type 1 allergy)
lower airway obstruction - wheeze (type 1 allergy)
allergens may be seasonal (pollens) or episodic (animal dander)
when symptoms are chronic, inflammation becomes established - cannot be explained by mast cell degranulation

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16
Q

immunological tightrope

A

self vs non self
dangerous infection vs commensal organisms
environmental allergens, food/pollen
activation for defence vs tolerance to prevent autoimmune and inflammatory diseases

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17
Q

origins of allergic disease

A

allergic/atopic math - progression of disease observed from infancy
eczema, food allergy, rhinitis, asthma
most children outgrow eczema and many food allergies
rhinitis/asthma may or may not be outgrown
allergic disease may present de novo in adults

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18
Q

chronic allergic inflammation: asthma

A

ongoing symptoms
most patients are sensitised to variety of airborne allergens
biopsy shows inflammatory infiltrate and airway changes (remodelling - thickened basement membrane, smooth muscle hyperplasia)
early allergic reaction phase does not provide good explanation by itself

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19
Q

late phase allergic reaction

A

early phase reaction is followed some hours later by a late phase reaction
biopsy of let tase shows infiltration with inflammatory cells
CD4 T cells, eosinophils, mast cells in particular
some insight into chronic allergic inflammation

20
Q

T cell subsets (CD4)

A

Th1 - releases IFN gamma
Th2 - releases IL-4,-5,-9,-13
Th17- releases IL-17
Treg - releases IL-10, contact dependent mechanisms

21
Q

Th2 hypothesis

A

Th2 responses to allergens consistently associated with allergic disease
biopsies of allergic inflammation are rich in T cells expressing Th2 cytokines

22
Q

why might Th2 be important in allergy?

A

IL-4 required for B cell class switching to IgE
IL-4 and IL-13 promotes mucus hypersecretion
IL-5 required for eosinophil survival
IL-9 recruits mast cells

23
Q

asthma acute responses

A

inflammatory mediators cause increased mucus secretion and smith muscle contraction - leads too airway obstruction
cells are recruited from the circulation

24
Q

asthma chronic responses

A

caused by cytokines and eosinophil products

25
Q

genetics

A

childhood allergy strongly predicted by parent with allergy

numerous genetic risk factors identified

26
Q

hygiene hypothesis

A

low hygiene levels, high pathogen load and helminth infection = immunity skewed to Th1, Treg cells induced
high hygiene levels, low pathogen load, no helminth infection = immunity skewed to Th2, reduced production of Treg cells

27
Q

detection of allergen specific IgE in vivo

A

skin prick testing
allergen extract applied as drops
top layers of epidermis punctured with lan net
wheal and flare response within 15 mins = positive
result needs interpretation in clinical context

28
Q

detection of allergen specific IgE in vitro

A

usually ELISA
purified allergen, stuck, incubated with sera
IgE antibodies in sera binds to allergen
immobilised IgE antibodies detected with detection antibody

29
Q

allergy treatment

A 
symptom relievers
drugs acting on early phase mediators
corticosteroids 
monoclonal antibodies 
immunotherapy
30
Q

allergy symptom relievers

A 
nasal decongestants 
-  eg. oxymetazoline 
- alpha 1 adrenoreceptors
- cause vasoconstriction 
- short term
b2 agonists
- eg salbutamol
- act on lung adrenoreceptors 
- cause smooth muscle relaxation 
adrenaline
- systemic adrenergic effects 
- oppose vasodilation  and bronchconstriction
31
Q

drugs acting on early phase mediators

A

mast cell stabilisers
H1 antihistamines
leukotriene receptor antagonists

32
Q

mast cell stabilisers

A 
eg sodium cromoglycate 
reduce mast cell degranulation (unknown mechanism)
topical only 
short half life 
main benefit = steroid free
33
Q

H1 antihistamines

A

inverse agonists at H1 histamine receptor
best used before exposure to allergen
1st generation: clorpheniramine (sedation, drug interactions)
2nd generation: cerizine, loratadine (minimal/no sedation)

34
Q

leukotriene receptor antagonists

A

only UK drug = montelukast
effective in reducing early allergic responses
inferior to H1 antihistamines
beneficial in chronic asthma

35
Q

corticosteroids

A

reduce immune activation
alter gene expression in T cells, B cells, and cells of the innate immune system
onset of action is delayed

36
Q

omalizumab

A

monoclonal antibody
directed against IgE
used for atopic asthma

37
Q

allergen specific immunotherapy

A

allergen doses administered by subcutaneous injection long term protection mainly venom allergy and rhinitis

38
Q

immunotherapy immunological effects

A 
induce Treg cell responses  to allergens 
reduce Th2 responses
induce allergen-specific IgG antibodies 
reduction in mast cell responsiveness
reduce allergen-specific IgE levels
39
Q

delayed type hypersensitivity

A

mediated by antigen specific effector T cells

40
Q

antigen specific definition

A

implies that a specific antigen stimulus is required, chichis them processed and presented to relevant T cells responsible for reaction

41
Q

effector T cell definition

A

T cells that have previously met antigen, and are ‘primed’ to produce a rapid and robust response

42
Q

contact dermatitis - sensitisation

A

molecules react with self proteins to create protein-hapten complexes
complexes are picked up by Langerhans cells which migrate to lymph nodes
Langerhans cells process and present antigen on MHC class II
in some individuals, complexes are recognised as foreign
activated T cells migrate to the dermis

43
Q

hapten

A

small molecule that cannot individually invoke an immune response, but can bind to protein to alter its immunogenicity

44
Q

contact dermatitis - elicitation

A

chemokines recruit macrophages
Th1 cells secrete IFN gamma (increases expression of vascular adhesion molecules, activates macrophages)
TNF alpha/beta stimulates local inflammation

45
Q

poison ivy

A

poison ivy lipid can cross skin and modify intracellular proteins
proteins are processed and presented on MHC class I to T cells
causes contact dermatitis
not everyone is susceptible

46
Q

patch testing for contact dermatitis

A

antigen impregnated patch placed on back
nickel, chrome, epoxy resin etc
read after 2 days

204 theme 1 (12 decks)

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