Hypersensitivity Type I and II

Question 1

What causes type I hypersensitivity reactions?

Answer 1

Allergens

Question 2

What is an allergen?

Answer 2

An antigen which elicits an immediate allergic reaction

Question 3

Which type of antibody is assciated with type I hypersensitivity reactions?

Answer 3

IgE

Question 4

How many receptors bind IgE?

Answer 4

2

Question 5

Typically what is IgE associated with?

Answer 5

Control of parasitic infection

Question 6

What receptors bind to IgE?

Answer 6

• FcεRII (low affinity receptor)
• FcεRI (high affinity receptor)

Question 7

How much IgE is usually bound to FCεR1?

Answer 7

The receptors are usually saturated with IgE despite a low IgE concentration in the serum as they bind with high affinity

Question 8

How can a type 1 hypersensititivity reaction lead to anaphylaxis?

Answer 8

• Becomes systemic
• Blood pressure falls
• Bronchospasm

Question 9

How are mast cells activated by IgE?

Answer 9

• Only activated if IgE is crosslnked by a specific allergen
• Triggers degranulation of mast cell and an inflammatory response

Question 10

Why is IgE mediated mast cell activation beneficial?

Answer 10

• Can rapidly recruit other leukocytes upon infection
• Inflammatin induced causing increased flow of lymph
• Chemical mediators cause smooth muscle contraction which can help expel pathigens from lung and/or gut

Question 11

What causes class switching of B cells to produce IgE?

Answer 11

Induction by Th2 T cells

Question 12

How do inhaled corticosteroids help treat asthma?

Answer 12

Block the delayed response in the lung, inhibiting influx of eosinophils, basophils, lymphocytes

Question 13

What antibodies mediate a type II hypersensitivity reaction?

Answer 13

IgG and IgM

Question 14

Where do antibodies bind in type II hypersensitivity reactions?

Answer 14

To cells/components of ECM

Question 15

What is the major difference between type II and III hypersensitivity reactions?

Answer 15

In type II the antibodies bind to antigen on a cell/component of ECM but in type III antibodies bind to a soluable antigen

Question 16

What does the classical complement cascade lead to activation of?

Answer 16

Membrane attack complex

Question 17

What are the 3 main mechanisms of tissue damage which occur in a type II Hypersensitivity reaction?

Answer 17

1. Phagocytosis
2. Antibody dependent cellular cytotoxicity
3. Classical complement cascade

Question 18

How does phagocytosis become frustrated in type II hypersensitivity reactions?

Answer 18

• Binding to FcR and complement R activates phagocytosis
• Leads to lysosomal contents being exocytosed and necrosis at site of reaction

Question 19

What happens in transfusion reactions?

Answer 19

• Type II hypersensitvity
• Extensive destruction of donor blood cells
• Results in fever, vomiting

Question 20

What type of antibody causes transfusion reactions?

Answer 20

IgM

Question 21

What type of antibody causes haemolytic disease of foetus and newborn?

Answer 21

IgG

Question 22

How is haemlytic disease of foetus and newborn prevented?

Answer 22

• Anti-RhD antibodies are injected in RhD mother at 28 weeks and after birth
• Binds to foetal RBCs, eliminating them and preventing maternal sensitisation

Question 23

What is autoimmune haemolytic anaemia?

Answer 23

Antibodies against patient’s own erythrocyte antigens can arise spontaneously or be induced by drugs

Question 24

How can drugs cause autoimmune haemolytic anaemia?

Answer 24

• Drug binds to RBCs
• Antibodies produced against drug
• Drug:antibody complexes bind RBC

Question 25

What causes myasthema gravis?

Answer 25

• IgG antibodies bind to Acetyl choline receptors and block acetyl choline from binding