Type 1 Hypersensitivity and Anaphylactic Shock

Question 1

What is meant by ‘atopy’?

Answer 1

This is the predisposition to make IgE to common environmental antigens

Question 2

What are the cells of the innate immune system?

Answer 2

Neutrophils, monocytes (macrophages on activation), eosinophils and mast cells

Question 3

What are the cells of the adaptive immune system?

Answer 3

B and T lymphocytes

Question 4

What is clonal deletion?

Answer 4

Where lymphocytes in the thymus (T cells) or bone marrow (B cells) are maturing, and they are tested for autoimmune response, if they cause a reaction to self-antigens then they are destroyed

Question 5

What is clonal expansion?

Answer 5

In a clonal expansion of lymphocytes, all progeny share the same antigen specificity in order to elicit a greater binding and thus immune response to the foreign antigen

Question 6

What are the differences between T and B lymphocytes?

Answer 6

B lymphocytes are produced in the bone marrow and not the thymus gland, and can bind to antigens directly via their antibody receptors whereas T cells have to bind to antigens presented by APCs

Question 7

What molecule acts as an antigen receptor on B cells?

Answer 7

Antibodies act as the antigen receptor on B cells

Question 8

Where do B lymphocytes mature?

Answer 8

Bone marrow

Question 9

Where do T cells mature?

Answer 9

Thymus gland

Question 10

How do T cells recognise antigens?

Answer 10

They only recognise antigens once they are presented by APCs as their own receptor secretion is very little

Question 11

How do innate immune cells bind to foreign antigens?

Answer 11

They can bind antibodies to their cell surface via the Fc receptor and use the antibody specificity to facilitate binding.

Question 12

Which type of antibody can pass across the placenta?

Answer 12

IgG

Question 13

What is the action of IgG antibodies presented by innate immune cells?

Answer 13

This can block pathogen binding, active complement and activate opsonisation to prepare the antigens/pathogens for phagocytosis

Question 14

What is the action of IgM antibodies presented by innate immune cells?

Answer 14

Block pathogen binding and activate complement

Question 15

What is the action of IgA antibodies presented by innate immune cells?

Answer 15

This antibody blocks pathogen binding and is present in many secretions such as tears and digestive juices

Question 16

What is the action of IgE antibodies presented by innate immune cells?

Answer 16

Binding to this antibody activates mast cells

Question 17

How may mast cells and/or basophils be activated?

Answer 17

> Via cross-linking of surface IgE on their surface antigens
Complement activation by C3a and C5a
Substance P or directly from nerves
Direct contact with pathogen

Question 18

Which complement factors can activate mast cells and basophils?

Answer 18

C3a and C5a

Question 19

What is the action of histamine produced as result of type 1 hypersensitivity?

Answer 19

> Increases permeability of the post-capillary venues
Vasodilates arterioles
Causes contraction of some smooth muscle e.g. bronchial
Increases itch

Question 20

What is the action of leukotrienes that are produced as result of type 1 hypersensitivity?

Answer 20

> Increase permeability of post-capillary venules

> Facilitates chemotaxis (increases inflammation)

Question 21

What is the action of prostaglandin produced as result of type 1 hypersensitivity?

Answer 21

> Arteriolar dilatation
Pain
Fever production

Question 22

What is the pathophysiology behind type 1 hypersensitivity?

Answer 22

This type of hypersensitivity involves mast cell activation which leads to the release of mediators such as histamine, leukotrienes and prostaglandins.

Question 23

What is anaphylactic shock?

Answer 23

Where there is systemic manifestation of allergic reaction that leads to systemic vasodilation and therefore shock due to insufficient cardiac output

Question 24

What causes the drop in blood pressure in anaphylactic shock?

Answer 24

Due to the increased permeability of the post-capillary venues as result of histamine and leukotriene release in allergic response, there is leakage of fluid into the interstitial space

Question 25

What is urtricaria?

Answer 25

This is also known as his and is is a raised, itchy red rash that is caused by inflammation of the skin dermis

Question 26

What is angiodema?

Answer 26

This is swelling in the subcutaneous tissue

Question 27

What may trigger anaphylaxis?

Answer 27

Certain antibiotics (beta lactams), aspirin, NSAIDS, anaesthetics, latex, foods, bee stings (arthropod venom) and exercise perhaps

Question 28

What drugs may trigger anaphylactic reaction?

Answer 28

Beta lactams, monobactams (antibiotics), aspirin, NSAIDS and anaesthetics

Question 29

How is anaphylactic shock treated?

Answer 29

Adrenaline given (to increase sympathetic tone and cause vasoconstriction to increase blood pressure and venous return to the heart), oxygen is given (in case there is airway obstruction), antihistamine, fluid IV and hydrocortisone (cortisol analogue which will increase water retention to increase blood volume and thus BP)