Allergy

Question 1

What are type I hypersensitivity reactions?

Answer 1

IgE mediated reactions in response to allergens. They occur within minutes and will cause mast cell degranulation and eosinophi activation.

Question 2

What are type II hypersensitivity reactions?

Answer 2

This is an autoimmune cytotoxic reaction between cell bound antigen and IgM or IgG antibodies. Will develop after the antibody is prodcued and will remain as long as the antigen remains. An example is autoimmune haemolytic anaemia

Question 3

What are type III hypersensitivity reactions?

Answer 3

It is an immune-complex reaction between circulating soluable antigens and IgG antibodys

Question 4

What is a type IV hypersensitvity reaction?

Answer 4

Cellular immune response by lymphocytes, reaction occurs greater than 4 hours after exposure. e.g. topical dermatitis

Question 5

Where are the IgE producing plasma cells for type I reactions mainly situated?

Answer 5

In the mucosal lympoid tissues adjacent to the respiratory and GI tracts

Question 6

What are the stages of a type I hypersensitivity reaction?

Answer 6

Exposure to the allergen
Sensitisation and IgE production
Re-eposure to the allergen producing the response

Question 7

What investigations can be done in allergy?

Answer 7

Serum specific IgE antibodies can be measured (RAST) this can be used to confirm a history
Skin prick testing for specific allergens however has a high false positive
Total IgE levels

Question 8

What effects does histamine release have on the body?

Answer 8

Increased blood flow
Increased vascular permeability
Contraction of extravascular smooth muscle
Stimulation of nerves causing itching

Question 9

What can be measured in the blood that is important for Diagnosing anaphylactic shock?

Answer 9

Tryptase levels rise in the blood after massive mast cell degranulation

Question 10

How do eosinophils damage tissues in allergy?

Answer 10

They are attracted by Il-5 and when they bind to cross linked immunocomplex this causes release of cytotoxic proteins that damage tissues

Question 11

What is the treatment for anaphylaxis?

Answer 11

500micrograms of adrenaline (0.5mls of 1/1000 adrenaline) This can be given every 10-15mins if needed
Maintain airway
Hydrocortisone can be given to help prevent the biphasic reaction

Question 12

What is oral allergy syndrome?

Answer 12

Can be mistaken for food allergy as there is swelling but it is not systemic. This causes IgE antibodies in the mouth to react to food pollens, but it is only local

Question 13

Why are drug reactions typically not type I hypersensitivity?

Answer 13

Drug molecules are generally too small to act as whole antigens

Question 14

What is urticaria?

Answer 14

Eruption of migrating itchy wheals that occur as a result of histmine activation. Angiooedema is the deeper version of this and they can often occur together. Urticaria can occur spontaneously and is not always an allergy

Question 15

What is the treatment for chronic spontaneous urticaria?

Answer 15

This is usually through strong antihistamines but in more serious cases can be cyclosporine and anti-IgE therapy

Question 16

What are atopic conditions and give some examples?

Answer 16

More chronic conditions associated with destruction of tissues, involve eosinophils, TH2 cells and mast cells
Extrinsic allergic asthma, hayfever and eczema

Question 17

What type of asthma are most childhood asthmas?

Answer 17

They are mostly extrinsic allergic asthmas, can be caused by dust mites, animals and pollens

Question 18

What causes the biphasic response in allergic asthma?

Answer 18

Initial response due to histamine release and other pre formed mediators in respiratory mucosa. Later the second response is due to lymphocytes and granulocytes infiltrating and causing further inflammatory mediator release

Question 19

Why do people with hay fever (atopic rhinitis) have greater risk of bacerial infections?

Answer 19

The oedema can cause blockage of the sinuses and eustatian tubes hence predisposing to secondary infection

Question 20

What is the treatment for hayfever?

Answer 20

Using potent H1 receptor antagonists

Leukotriene receptor antagonists and anticholinergics can also be given in severe cases

Question 21

What tests can be used to confirm allergic eczema?

Answer 21

Serum IgE is often raised, positive skin prick test to various antigens. Thought to be caused by T cells and S. aureus super antigens.

Question 22

What are some examples of delayed hypersensitivity reactions (type IV)?

Answer 22

Contact dermatits
Coeliac disease
Sarcoidosis
Granulomatous TB

Question 23

What is contact dermatitis?

Answer 23

Delayed hypersesitivity reaction that superficially resembles atopic eczema but is due to cell mediated inflammatory condition. Can be caused by nickel or copper

Question 24

What sort of allergy is coeliac?

Answer 24

There are IgA antibodies specific to gluten
It is diagnosed through an initiaal screen of transglutaminase antibodies, transglutaminase enzymes are present in healthy individuals for breakdown of gluten