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Path - Immunology > Allergy > Flashcards

Allergy Flashcards

(44 cards)

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1
Q

What is an allergic disorder?

A

Immunological process resulting in immediate and reproducible symptoms after antigen exposure

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2
Q

What is an allergen?

A

A harmless substance that triggers an IgE mediated immune response and causes clinical symptoms

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3
Q

What is sensitisation?

A

Detection of specific IgE by testing (skin prick/in vitro blood test)

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4
Q

What does sensitisation show?

A

RISK of allergic disease
does NOT define allergic disease
So NECESSARY but NOT sufficient to cause allergy

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5
Q

What do allergens/venoms/helminths activate?

A

Cytokines:

  • IL-1alpha
  • IL25
  • IL33
  • TSLP
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6
Q

What do allergen cytokines activate?

A

Th2 cells (MAINLY)
Th9
ILC2

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7
Q

What are the Th2 effector cytokines?

What do they activate?

A

IL4
IL5
IL9
IL13

They activate eosinophils and basophils

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8
Q

Explain the tfh2 cell pathway

A

allergen > signalling cytokines > Tfh2 > IL4, IL21 > B cells >IgE, IgG4 > IgE cross links mast cell > histamine, leukotriene, prostaglandin release

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9
Q

What do histamines, leukotrienes, prostaglandins act ion?

A

Endothelium > increase permeability
Smooth muscles > smooth muscle contraction
Neurons>itching

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10
Q

What is a risk factor for IgE antibody development / sensitisation ?

A

Skin defect e.g. atopic dermatitis
as it allows allergen entry
Skin dendritic. cells promote Th2 cytokine secretion much more efficiently than other dendritic subtypes

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11
Q

What kind of exposure induces immune tolerance?

A

oral exposure

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12
Q

How does oral/Gi exposure promote immune tolerance?

A

Because Tregs from the GI mucosa inhibits IgE synthesis

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13
Q

What is the function of eosinophil?

A

Host defence against parasites, bacteria, viruses

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14
Q

What is the key cytokine for eosinophil development and expansion?

A

IL-5

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15
Q

What is normal IgE function?

A

To protect against helminth and parasitic infection

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16
Q

What is an unwanted effect of IgE function?

A

mast and basophil degranulation, associated to immediate hypersensitivity reaction

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17
Q

What are the 2 subtypes of mass cells in humans?

A

MC tryptase T in skin

MC chemotryptase CT in airway

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18
Q

What is mast cell degranulation triggered by?

Study These Flashcards
A

IgE/IgG receptors

G protein coupled receptors

19
Q

Explain mast cell/basophil degranulation

Study These Flashcards
A

Cross linking of bound IgE > histamine, leukotriene, prostaglandin release

mast cell degranulation leads to:

  • recruitment of soluble proteins and inflammatory cells to site of infection
  • increase in rate of lymphatic flow back to regional lymph nodes
  • smooth muscle contraction in lungs, gut
20
Q

Factors that promote IgE production

Study These Flashcards
A

Antigen dose
length of exposure
physical properties of antigen (source, water solubility, carbohydrates, resistance to heat/digestive enzymes)
route of exposure

21
Q

What is the order of age of onset for allergic diseases?

Study These Flashcards
A

Infants: atopic dermatitis, food allerggy
Childhood: asthma, allergic rhinitis
Adults: drug allergy, bee allergy

22
Q

what are the theories for increased prevalence of allergic disorders?

Study These Flashcards
A 
Hygiene hypothesis 
Increased childhood vaccination, exposure to antibiotics, 
lack of vitamin D in infancy 
Dietary factors 
Alteration in intestinal microbiome 
High concentration of dietary sugars
23
Q

What are clinical features of IgE mediated response?

Study These Flashcards
A

MIN 2 ORGANS INVOLVED
SYMPTOMS MUST BE REPRODUCIBLE
SKIN: angioedema, urticaria flushing, itching
RESP: cough, SOB, nasal congestion, wheeze, red watery eye
GI: nausea, diahrroea, vomiting, hypotension

24
Q

What is evidence that the microbiomial environment can protect against asthma?

Study These Flashcards
A

Amish vs Hutterite communities

Amish have lower asthma prevalence as there is higher LPS prevalence in dust samples in Amish homes

25
What co-factors can trigger allergic symptoms?
Exercise Alcohol NSAID Viral infection
26
What allergen specific IgE (sensitisation) tests can you do?
Skin prick test (SPT) Intradermal test IgE blood test
27
What does a skin prick test do?
Exposes pt to allergen extract solution through skin prick on arm Looks for cross linking of IgE on skin mast cells > degranulation > release of histamine and other inflammatory mediators
28
What controls do you use for a skin prick test?
``` POSITIVE control (histamine) NEGATIVE control (dilutent) ```
29
How do you identify a positive result in a skin prick test?
wheal >3mm greater than positive control
30
What should you discontinue before SPT?
antihistamines /antidepressants containing antihistamine | for 48h prior
31
how do intradermal test work?
same principle as skinprick | allergen is now injected into intradermal layer
32
When are intradermal tests indicated?
To follow up negative venom or drug allergy test | If SPT is negative but story is convincing
33
What is the benefit of SPT?
Excellent negative predictive value (no false neg)
34
What is the benefit of intradermal test?
Excellent positive predictive value (no false positive)
35
What are indications for IgE blood test?
``` No access to SPT/IDT Patient can't stop antihistamine Patient has dermatographism (skin can't be scratched) Patient has excessive eczema Hx of anaphylaxis Borderline SPT results ```
36
What is increased serum tryptase a marker for?
systemic degranulation of mast cells during anaphylaxis
37
When is it good to get a serum tryptase?
if anaphylaxis dx is uncertain e.g. during anasthesia pt becomes hypotensive with rash
38
What is a food allergy?
An adverse health effect arising from specific immune response that occurs reproducibly on exposure to a given food
39
What is a food intolerance?
non-immune reaction that includes metabolic, pharmacological, unknown mechanism
40
What is an important risk factor for food allergy in children?
Atopic dermatitis
41
Which investigation is best to CONFIRM anaphylaxis is occurring
Tryptase
42
how do tryptase levels in anaphylaxis change over time
peaks at 1-2h | back to baseline in 6-12h
43
what are allergy tests you can do as elective?
``` SKin prick Intradermal Allergen specific IgE Basophil activation test Challenge test ```
44
What are allergy tests you should do during acute episode?
Mast cell tryptase Blood/urine histamine -- looks for evidence of mast cell degranulation --

Path - Immunology (11 decks)

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