Anaphylaxis

Question 1

What is anaphylaxis?

Answer 1

An acute (immediate) hypersensitivity reaction that can be systemic, and is sometimes so overwhelming that it is life threatening.
- It results from a response to an allergen that is present throughout the body

Question 2

What are some substances that can cause anaphylaxis?

Answer 2

Substances which can cause anaphylaxis in susceptible patients are those which can pass freely around the body

• Penicillin, especially if it has previously been given intravenously
• Certain other drugs (e.g. local anaesthetics, x-ray contrast agents)
• Venom in bee or wasp stings
• Peanuts- the allergen can be absorbed fast enough to cause systemic effects

Question 3

What type of cell causes anaphylactic symptoms?

Answer 3

Mast cells

Question 4

What binds to mast cells?

Answer 4

IgE

Question 5

Where do mast cells mature?

Answer 5

they are released as progenitor from the bone marrow, and it homes to connective and mucosal tissues where it matures

Question 6

How are mast cells distributed in body?

Answer 6

Mast cells are widely distributed throughout the body both in connective tissue (e.g. under the skin) and in association with epithelial mucosae (e.g. the respiratory and intestinal epithelia)

Question 7

What do mast cells contain?

Answer 7

They contain prominent granules which contain a number of mediators of inflammation, notably histamine and leukotrienes

Question 8

What are the main signalling molecules involved in anaphylaxis?

Answer 8

Histamines and leukotrienes

Question 9

What do the inflammatory mediators released by mast cells principally work on?

Answer 9

on blood vessels and smooth muscle

Question 10

What do histamines do to connective tissue and mucosae?

Answer 10

In connective tissue histamine causes dilation of vessels with increased blood flow to the surface and increased movement of fluid out of the blood stream (oedema)
Around mucosae the opposite effect occurs- causing constriction of airways and contraction of the smooth muscle in the walls of the intestines

The net effect depends on whether the stimulation is local or systemic

Question 11

What are the symptoms of acute allergic reactions? (4)

Answer 11

Wheezing, urticaria, sneezing/ rhinorrhea, conjunctivitis

Question 12

What is an acute allergic reaction?

Answer 12

Allergen specific IgE is pre-bound to the FcR1 receptor on mast cells. Circulating allergen binds the IgE causing receptor cross linking and mast cell degranulation.

Question 13

What are the symptoms of a chronic allergic reaction? (3)

Answer 13

Further wheezing, sustained blockage of the nose, eczema

Question 14

What happens in a chronic allergic reaction?

Answer 14

Recruitment and activation of allergen specific T cells and other cells by mast cells derived mediators

Question 15

How are IgE produced?

Answer 15

The CD4 T helper cells causes a class switch to IgE production

Question 16

What is an allergen?

Answer 16

An antigen which causes an allergic type IgE-mediated response

Question 17

What causes rashes and puffy skin seen in anaphylaxis?

Answer 17

Histamine causes vasodilation leading to red skin colour and oedema leading to raised appearance

Question 18

What is skin rash called?

Answer 18

urticaria

Question 19

When can the localised skin reaction seen in allergy be useful?

Answer 19

In skin prick tests to see if they caused a wheal-and-flare reaction

Question 20

What is hay fever called?

Answer 20

Allergic Rhinitis

Question 21

What causes Allergic Rhinitis?

Answer 21

Odema in the epithelia lining the nose resulting in general irritation and stimulation of mucus secretion

Question 22

What causes asthma?

Answer 22

When the allergen reaches the bronchioles of the lungs, resulting in contraction of smooth muscles which reduces the diameter of the airways, leads to increased mucus production and difficulty breathing in and out

Question 23

What causes food allergies?

Answer 23

When an allergen is ingested, it acts on the mucosal mast cells in the intestinal tract - leading to vomiting and diarrhoea

if absorbed into bloodstream, can cause rashes or itching

Question 24

What occurs in anaphylaxis which can be fatal and affect organ function?

Answer 24

A rapid decrease in blood pressure as the blood vessels dilate

Question 25

Why is adrenaline (epinephrine) given as an emergency treatment for anaphylaxis?

Answer 25

Epinephrine is a vasoconstrictor and therefore is aimed at trying to stabilize blood pressure

Question 26

After adrenaline, what medication is given following an anaphylactic shock?

Answer 26

Anti-histamines and anti-inflammatory corticosteroids like hydrocortisone

Question 27

Why do patients feel faint follow an anaphylactic shock?

Answer 27

Due to the dramatic loss of blood pressure - hypotension

Question 28

Why is blood pressure carefully measured after a shock?

Answer 28

Provides a reliable indication of recovery

Question 29

What is biphasic anaphylaxis?

Answer 29

When the symptoms return within hours of the initial reaction

Question 30

How long should patients with moderate respiratory/cardiovascular compromise should be observed before discharge?

Answer 30

8-10 hours

Question 31

What immunoglobulin is likely to be involved in anaphilaxys?

Answer 31

- Immunoglobulin E - Histamine and leukotrienes are secreted following antigen binding to the cell surface IgE - The IgE response is thought to be important in defence against certain parasitic infections (e.g. nematodes) - However, it can occur inappropriately to give rise to allergic reactions - In type I hypersensitivity, activation of CD4+ T helper cells (TH2) causes a switch to IgE production

Question 32

What causes anaphylaxis?

Answer 32

- IgE becomes bound to specific binding sites (IgE-receptors) found on the surface of mast cells - And it is the subsequent stimulation of these cells by exposure to the antigen that causes allergic or anaphylactic responses - An antigen that causes an allergic type of IgE-mediated response is often known as an allergen

Question 33

What is the usual pathway when an antibody attaches to a cell?

Answer 33

- The normal pathway of lymphocyte activation occurs where antigen binds to the surface IgM on lymphocytes to stimulate proliferation and secretion of antibody - Usually the antibody initially secreted is IgM - And this switches to IgG as the immune response progresses

Question 34

What is an oedema?

Answer 34

build up of fluid which causes the affected tissue to swell up

Question 35

What causes the rashes and puffy skin?

Answer 35

If the patient has a skin allergy, stimulation of connective tissue mast cells causes vasodilation leading to the red colour of the skin rash, and oedema leading to its raised appearance - This type of rash is often called urticaria and is familiar as the pattern of rash caused by stinging nettles

Question 36

What can cause skin allergies?

Answer 36

Substances known to be capable of causing skin allergies include animal hair, proteins in natural latex, certain chemicals, substances in insect and plant stings

Question 37

What causes hay fever and asthma?

Answer 37

If the allergen is inhaled the principal site of action will be mucosal mast cells of the respiratory system If this is principally in the nasal passage, the effect will be oedema in the epithelia lining the nose and a consequent general irritation including stimulation of mucus secretion It is the allergic reaction which causes hay fever (allergic rhinitis) If the allergen reaches the bronchioles of the lungs then there will be contraction of smooth muscle reducing the diameter of the airways, as well as inflammation and increased mucus production The result is asthma, with difficulty breathing in and (especially) breathing out

Question 38

What are substances that are known to cause asthma/ hay fever?

Answer 38

Substances known to be capable of causing hay fever and asthma include pollens, faeces of dust mites, and proteins from animal hairs

Question 39

What causes food allergies?

Answer 39

If the allergen is ingested, then it will act at mucosal mast cells in the intestinal tract - The stimulation of the associated smooth muscle leads to the vomiting and diarrhoea typical of a food allergy - If the allergic substance can be absorbed and pass into the bloodstream it may also cause skin symptoms (rashes or itching)

Question 40

What substances are known to cause food allergies?

Answer 40

Substances known to be capable of causing food allergies include peanuts and other nuts and legumes (e.g. soya), shellfish, milk, eggs, wheat

Question 41

What is shock?

Answer 41

a dramatic drop in blood pressure which can affect organ function

Question 42

How does the patient respond to constriction of bronchi?

Answer 42

Increase in both respiratory and heart rates There may also be symptoms of nausea, abdominal cramps, or diarrhoea from the effects on the intestine

Question 43

What is emergency treatment aimed at?

Answer 43

initially at the loss of blood pressure (hypotension) And then underlying inflammation

Question 44

What do they do to patient with anaphylaxis?

Answer 44

The patient is lain down with feet raised in order to improve blood supply to the head and trunk An injection of adrenaline will act to constrict peripheral blood vessels and redirect blood to the organs

Question 45

Why does an anaphylactic patient feel faint?

Answer 45

Due to the dramatic drop in blood pressure (hypotension) Syncope (fainting) is a temporary loss of consciousness usually related to insufficient blood flow to the brain They are was initially laid down on a couch with his legs raised to counteract this

Question 46

What is long-term treatment for anaphylaxis/ allergies?

Answer 46

Avoid known allergens For those difficult to avoid completely (such as wasp stings, or nuts where small traces may contaminate apparently innocent foods) the patient may be given adrenaline in a self-injection "pen" e.g. EpiPen

Question 47

What happens if a breathing problem persists with anaphylaxis?

Answer 47

oxygen may be necessary and bronchodilators may be given via an inhaler e.g., salbutamol

Question 48

What is an example of an anti-inflammatory corticosteroid?

Answer 48

hydroxycorticosterone

Question 49

Why was blood pressure monitored in hospital for the anaphylactic patient?

Answer 49

Monitoring of blood pressure provides a reliable indication of recovery Occasionally the symptoms return (usually within hours of the initial reaction) This is known as biphasic anaphylaxis Patients with moderate respiratory or cardiovascular compromise should be observed for up to 8-10 hours before discharge