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MCDone > Hypersensitivity and Allergy > Flashcards

Hypersensitivity and Allergy Flashcards

1
Q

What are hypersensitivity reactions usually mounted against?

A

Harmless foreign antigens
Autoantigens
Alloantigens- antigens from other individuals of same species, eg- transfusions

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2
Q

What are the four type of hypersensitivity reaction?

A

Type 1 – immediate hypersensitivity
Type 2 – antibody-mediated cytotoxicity
Type 3 – immune complex mediated
Type 4 – delayed cell mediated

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3
Q

Describe the mechanism of type 1 hypersensitivity?

A

On 1st exposure you get sensitisation – IgE is produced, which binds to mast cells and basophils
On second exposure, antigen cross-links the IgE on the mast cells causing degranulation and release of inflammatory mediators

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4
Q

What types of diseases are examples of type 2 hypersensitivity?

A

Organ specific autoimmune diseases: e.g. myasthenia gravis, glomerulonephritis, pemphigus vulgaris, pernicious anaemia
Autoimmune cytopenias e.g. autoimmune haemolytic anaemia, thrombocytopenia, neutropenia

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5
Q

What are the consequences of immune complex formation in type 3 hypersensitivity?

A

Formation of antigen-antibody complexes in the blood which deposit in tissues and activate complement and cause cell recruitment
This can cause tissue damage such as vasculitis

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6
Q

Give some examples of diseases caused by delayed type hypersensitivity.

A

Chronic graft rejections
Graft-versus-host disease
Coeliac disease

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7
Q

Describe the mechanism of delayed type hypersensitivity.

A

The transient/persistent antigen is presented to T cells, which then activate macrophages and CTLs
Activated macrophages produce TNF-alpha, which is responsible for much of the tissue damage

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8
Q

What is atopy?

A

A form of allergy in which there is a hereditary or constitutional tendency to develop hypersensitivity reactions in response to allergens

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9
Q

How common is atopy?

A

Very common – about 50% of young adults in the UK

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10
Q

List some genetic risk factors of atopy.

A

The genetic component is polygenic but genes of the IL-4 cluster and genes on chromosome 11q have been linked to atopy

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11
Q

Among which age group is atopy most common?

A

Teens

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12
Q

Describe the gender difference in asthma

A

Males – asthma in childhood is more common

Females – asthma in adulthood is more common

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13
Q

What other environmental factors affect atopy?

A

Family size, infections, animals, diet, age

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14
Q

What type of hypersensitivity is responsible for anaphylaxis, urticaria and angioedema?

A

Type 1 hypersensitivity

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15
Q

What type of hypersensitivity is responsible for chronic urticaria?

A

Type 2 hypersensitivity

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16
Q

What type of hypersensitivity is responsible for asthma, rhinitis and eczema?

A

Type 1 and type 4 hypersensitivity

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17
Q

Describe sensitisation in atopic airway disease.

A

T cells are naïve before they have seen their antigen
Once the T cells are exposed to the antigen by APCs such as dendritic cells, they can become Th1 cells (producing IFN-gamma), T regs or Th2 cells. In hypersensitivity the Th2 route is the more dominant. The Th2 cells lead to the activation of B cells to antibody producing plasma cells by IL-4 and 13 which leads to the production of IgE antibodies.

18
Q

Describe what happens in second exposure to the allergen.

A

In second exposure, the allergens are presented by APCs to memory Th2 cells, which then release IL-5, which causes eosinophil degranulation.
Th2 cells also release IL-4 and IL-13, which stimulate production of IgE by plasma cells.
The antigens crosslink the IgE on the surface of mast cells causing degranulation

19
Q

What percentage of blood leukocytes are eosinophils?

A

2-5%

20
Q

Describe the appearance of the nucleus of eosinophils.

A

Bilobed

21
Q

What receptors do mast cells have on their cell surface?

A

IgE receptors

22
Q

What mediators are released by mast cells?

A

Preformed: histamines, cytokines, toxic proteins

Newly synthesised: leukotrienes, prostaglandins

23
Q

What percentage of blood leukocytes are neutrophils?

A

55-60%

24
Q

What three processes cause airway narrowing in an acute asthma attack?

A

Vascular leakage leading to airways wall oedema
Mucus secretion fills up the lumen
Smooth muscle contraction around the bronchi

25
Q

Describe the changes seen in a patient with chronic asthma.

A

The lumen of the airway is narrowed and the airway wall is grossly thickened
There will be cellular infiltration by Th2 lymphocytes and eosinophils
There will be smooth muscle hypertrophy, mucus plugging, epithelial shedding and subepithelial fibrosis

26
Q

State some important clinical features of asthma.

A 
Chronic episodic wheeze 
Bronchial hyperresponsiveness  
Cough 
Mucus production  
Breathlessness  
Reduced and variable peak expiratory flow (PEF)
27
Q

What can allergic eczema lead to sensitisation of?

A

House dust mites – their proteins can get through dry, cracked skin

28
Q

What type of hypersensitivity is food allergy?

A

Type 1 hypersensitivity (IgE)

29
Q

What are the symptoms of a mild reaction to a food allergy?

A

Itchy lips and mouth
Angioedema
Urticaria

30
Q

What are the symptoms of a severe reaction to a food allergy?

A

Nausea
Abdominal pain
Diarrhoea
Anaphylaxis

31
Q

What is anaphylaxis?

A

Severe generalised allergic reaction

32
Q

What is anaphylaxis caused by?

A

Generalised degranulation of IgE sensitised mast cells

33
Q

State some symptoms of anaphylaxis.

A 
Itchiness around mouth, pharynx and lips  
Swelling of the lips and throat  
Wheeze, chest tightness, dyspnoea 
Faintness, collapse  
Diarrhoea and vomiting
34
Q

How can you test for allergies?

A

Skin prick test

35
Q

What is the emergency treatment of anaphylaxis?

A

Adrenaline

36
Q

Describe the step-by-step treatment of asthma.

A

Step 1: short acting beta 2 agonist (e.g. salbutamol)
Step 2: low-moderate dose inhaled steroids (e.g. beclomethasone, budesonide, fluticasone)
Step 3: add long acting beta 2 agonist or a leukotriene receptorantagonist + high dose inhaled corticosteroids
Step 4: add courses of oral steroids

37
Q

What are the two types of immunotherapy that are used to develop tolerance in patients?

A 
Subcutaneous immunotherapy (SCIT) 
Sublingual immunotherapy (SLIT)
38
Q

4 types of hypersensitivity relating to the mediator

A

IgE
Anitbodies- IgG
Immune complexes
T cells

39
Q

Diseases associated with T1 hypersensitivity

A 
Anaphylaxis
Asthma
Rhinitis
Food allergy
Seasonal or all year round particles
40
Q

Classification of allergic rhinitis

A

Seasonal- eg pollen

Perennial- eg pets

41
Q

Symptoms of allergic rhinitis

A

Sneezing
Itchy nose and eyes
Nasal blockage
Loss of smell and taste

MCDone (43 decks)

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