Case 34: A systemic type I hypersensitivity response

Question 1

What leads to the systemic manifestations associated with the immediate release of histamine and other inflammatory mediators in a type I hypersensitivity response?

Answer 1

Activation of mucosal mast cells and subsequent entry of allergens to the bloodstream

Question 2

What is inflammatory response to allergens mediated by?

Answer 2

IgE

Question 3

What is the sensitisation phase followed by?

Answer 3

Response

Question 4

What are the 2 different types of response possible in type I hypersensitivity?

Answer 4

Local (rhinitis, bronchoconstriction, conjunctivities) or systemic (anaphylaxis)

Question 5

What does allergen interaction with dendritic cells facilitate?

Answer 5

Differentiation to Th2 T cells that help B cell secretion of IgE

Question 6

Which cytokines do Th2 cells release when helping B cells?

Answer 6

IL-4 and IL-5

Question 7

What does Th2 cells releasing IL-4 and IL-5 act on?

Answer 7

Mast cells

Eosinophil activation

IgE production

Question 8

What does subsequent allergen exposure in type I sensitivity lead to?

Answer 8

Eliciation: degranulation of IgE loaded mast cells.

IgE binds mast cells in tissues by high affinity FceR
Allergen cross-links IgE on tissue mast cells
Degranulation
Release of histamine, leukotrienes, PGEs and cytokines

Question 9

What is the type of allergic response in type I hypersensitivity dependent on?

Answer 9

Tissue type

Question 10

How will the GIT tract respond in type I hypersensitivity?

Answer 10

Increased fluid secretion and peristalsis, leading to diarrhoea and vomiting

Question 11

How will the skin respond in type I hypersensitivity?

Answer 11

Increased fluid secretion and vasodilation leading to swelling, itching and urticaria

Question 12

How will the airways respond in type I hypersensitivity?

Answer 12

Bronchoconstriction and increased mucous production leading to nasal blockage, coughing, phlegm and asthma

Question 13

How will the blood vessels respond in type I hypersensitivity?

Answer 13

Increased blood flow and permeability leading to increased tissue fluid and cell infiltrate and anaphylactic shock

Question 14

What is the skin response seen with a skin prick test?

Answer 14

Wheal and flare

Question 15

What does skin prick test stimulate?

Answer 15

Immediate phase of the allergic response

Question 16

What happens during first exposure to the antigen in type I hypersensitivity?

Answer 16

Exposure to antigen → B cells produce IgE with help from dendritic cells → remain on mast cells and basophils

Question 17

What happens during second exposure to the antigen in type I hypersensitivity?

Answer 17

Allergen binds IgE on mast cells, causing degranulation → body flooded with histamine → vasodilation, etc.

Question 18

How can a type I allergic reaction be treated?

Answer 18

Adrenaline: bronchodilator and vasoconstrictor - beta-2 agonist

Oxygen mask

Antihistamines

Anti-inflammatories

Question 19

Why would a patient with type I allergic reaction be admitted to hospital overnight even though they show significant improvement?

Answer 19

Delayed response can happen - late mediators

Eosinophils and cytokines that cause granulation can appear 8-12 hours after the initial response.