Allergy + Hypersensitivity

Question 1

What is hypersensitivity?

Answer 1

State of altered reactivity in which the body reacts with an exaggerated immune response to foreign antigen

Question 2

What type of reaction is type I?

Answer 2

IgE mediated

Question 3

What type of reaction is type II?

Answer 3

Non-IgE mediated
(Cytotoxic)

Question 4

What type of reaction is type III?

Answer 4

Non-IgE mediated
(Immune complex)

Question 5

What type of reaction is type IIII?

Answer 5

Non-IgE mediated
(Cell mediated)

Question 6

Describe type I

Answer 6

Most common
Allergen
Mild - life threatening

Question 7

What are some types of allergens?

Answer 7

Inhaled materials - eg. pollen
Injected materials - eg. drugs/vaccines
Ingested materials - eg. food
Contacted materials - eg. plant leaves

Question 8

What are allergens?

Answer 8

Antigens that initate an unwanted IgE-mediated reaction

Question 9

What is the role of IgE in health?

Answer 9

Plays role in protection
Rid body of metazoan parasites

Question 10

Describe the role of IgE in type I reaction?

Answer 10

IgE producing B cells activated during sensitisation (first exposure)
IgE binds to Fc receptor on mast cells or CD63 on basophils
IgE recognises allergen and next exposure binds rapidly and causes
immediate degranulation (elicitation)

Question 11

What do allergic reactions consist of?

Answer 11

Immediate reaction followed by late phase response (hours later)

Question 12

What is immediate reaction caused by?
Allergy

Answer 12

Direct effect of mast cell degranulation

Question 13

What is late phase response caused by?
Allergy

Answer 13

Continuous mediator production

Question 14

What is an example of type I reaction?

Answer 14

Atopic eczema

Question 15

What does atopic mean?

Answer 15

Genetic predisposition

Question 16

Describe eczema

Answer 16

Early years
Wide range of allergens
Pruritis (itching)

Question 17

Describe what happens for eczema to take place

Answer 17

Allergen has to pass through physical barrier of epidermis

Question 18

What is the predisposing factor of eczema?

Answer 18

Mutations in genes maintaining barrier function

Question 19

What is systemic anaphylaxis caused by?

Answer 19

Allergens that reach blood stream + activate mast cells

Question 20

What are the 3 potentially fatal reactions in systemic anaphylaxis?

Answer 20

Laryngeal oedema = suffocation
Bronchiole constriction = suffocation
Peripheral oedema = hypotension + heart attack

Question 21

What reaction can penicillin allergy elicit?

Answer 21

Type I
Type II

Question 22

What are the allergy tests?

Answer 22

Skin prick
Blood test
Patch test
Food challenge

Question 23

Describe the skin pick test

Answer 23

Skin pricked with a tiny amount of the suspected allergen
Skin around the prick will become itchy, red and a wheal will appear

Question 24

Describe blood test

Answer 24

Specific IgE test
Measures blood IgE antibody levels in response to allergen

Question 25

Describe patch test

Answer 25

Tests if skin reaction is due to contact with specific allergen *Small amount of allergen added to metal discs taped to your skin for 20 minutes and reaction monitored

Question 26

Describe food challenge

Answer 26

Diagnose food allergy Subject given gradually increasing amounts of the suspected food to which they are allergic and their reaction monitored Can only test one food at each appointment Has to be conducted in an ITU setting (danger to patient)

Question 27

What are the treatments for type I?

Answer 27

Avoid allergen Drugs Immunological treatment

Question 28

Describe treatment using drugs for type I

Answer 28

Antihistamines – compete with histamine for receptors Hydrocortisone – block histamine synthesis Cromoglycate – stabilises mast cells and stops histamine release Epinephrine – best immediate treatment for anaphylactic shock

Question 29

Describe the immunological treatment for type I

Answer 29

hyposensitisation – repeat injections of allergen May work by shifting from IgE to IgG production

Question 30

Describe histamine receptor blockers Antihistamines

Answer 30

Inverse agonists Stabilise receptor in inactive conformation Making excessive stimulation with histamine less possible

Question 31

Describe the stimulation of adrenoreceptors Epinephrine

Answer 31

Increases peripheral vascular resistance Improves blood pressure and coronary perfusion Decreases angioedema = bronchodilation Increases intracellular cAMP in mast cells + reduces release of inflammatory mediators

Question 32

Describe type II

Answer 32

Involves activation of complement by IgG or IgM binding to cell surface antigens

Question 33

What is an example of type II?

Answer 33

Haemolytic anemia

Question 34

What is haemolytic anaemia caused by?

Answer 34

Autoimmune haemolytic anaemia Blood group incompatibility Penicillin

Question 35

Describe type III

Answer 35

Mainly IgG responses + their pathogenesis

Question 36

What does type III involve?

Answer 36

Reactions against soluble antigens circulating in serum

Question 37

What does type III result in?

Answer 37

Inflammatory response leading to tissue injury

Question 38

What is the pathology of type III due to?

Answer 38

Antibody-antigen aggregates in tissues

Question 39

What are examples of type III?

Answer 39

Arthus reaction Serum sickness Oral erythema multiforme (EM)

Question 40

What is Arthus reaction caused by?

Answer 40

Intradermal injection/vaccination Ab-antigen (IgG) complexes deposited in tissues

Question 41

What happens in Arthus reaction?

Answer 41

Localised vasculitis response Complement activation + mast cell sensitisation via Fc receptors Activates phagocytes + localised inflammatory response

Question 42

What is serum sickness?

Answer 42

Systemic Arthus reaction = large quantities of injected antigen

Question 43

What are the symptoms of serum sickness?

Answer 43

Vasculitis Rash Fever Joint swelling/pain

Question 44

What is oral erythema multiforme (OEM)?

Answer 44

Crusty blistering of oral mucosa

Question 45

What is oral erythema multiforme (OEM) caused by?

Answer 45

Deposition of IgM in oral mucous membrane

Question 46

What is type IV directed by?

Answer 46

Pro-inflammatory mediators released by antigen specific T cells

Question 47

What are some type IV examples?

Answer 47

Type 1 diabetes Crohn's disease

Question 48

Describe type 1 diabetes with type IV reaction

Answer 48

Pancreatic beta cell antigen Consequence = beta cell destruction

Question 49

Describe Crohn's disease with type IV reaction

Answer 49

Antigens of intestinal microbiota Consequence = regional intestinal inflammation + scarring

Question 50

How is type IV (delayed) caused?

Answer 50

Excessive release of inflammatory mediators

Question 51

When can type IV occur?

Answer 51

In response to chemicals + metal ions

Question 52

What happens in type IV with nickel or chromate?

Answer 52

Metal ions can alter peptide binding to MHC Class II and promote a CD4+ Th1 response Nickel also activates TLR4 directly