18. Hypersensitivity

Question 1

What is a hypersensitivity?

Answer 1

Excessive immune responses in response to different antigens that can cause damage

Question 2

What is a cytokine storm

Answer 2

Activation of a high amount of CD4 molecules

Question 3

What are the most important cells in hypersensitivity reactions?

Answer 3

Th2 and mast cells

Question 4

What are the different types of allergic reactions that occur to dust in the lungs

Answer 4

IgE- acute reactions mimicking asthma and rhinitis

IgG- more prolonged, severe reaction mimicking farmers lung

Question 5

Explain the different types of hypersensitivity reactions?

Answer 5

Type 1- seconds, IgE releaased

Type 2- seconds if IgG is performed

Type 3- hours if IgG is performed

Type 4- 2-3 days, T cell mediated

Question 6

Explain type 1 hypersensitivity?

Answer 6

Mediated through the degranulation of mast cells and eoesinophils. The effects are felt within minutes of exposure. Causes immediate hypersensitivity, allergy

Th2 produces IL4, inducing B cells to produce IgE.

Can manifest as rhinitis, asthma, anaphylaxis, dermatitis

Question 7

What is urticaria

Answer 7

Small itchy swelling on the skin

Question 8

What is angioedema?

Answer 8

Non specified swelling

Question 9

Explain peanut allergies?

Answer 9

Most common food allergy, allergy to peanut protein Ara h2 a very stable protein causes systemic reactions. Allergy to h8 is cross reactive with other food not very stable

Question 10

What causes allergies?

Answer 10

Polymorphisms in the expression of the gene encoding filaggrin is established as a cause of allergy and is implicated in 50% of severe eczema

Question 11

Describe anaphylaxis

Answer 11

Most serious type of allergy
Mast cells produce prostaglandins and leukotrianes through the cycloocygenase and lipoxygdnas pathways
This increases vascular permeability and causes vasodilation
Mast cells produce histamine increasing the shift of fluids outside the vascular compartment

Question 12

How do you treat allergies?

Answer 12

Prevention
S
Desensitisation (small exposure to allergens over time)
Drug treatment: B2 adrenergic agonists, epinepherine ,antihistamines, corticosteroids

Question 13

How does a skin prick test work?

Answer 13

Skin is pricked with various antigens, boxes 1 and 2 are pricked with histamine (known reaction) and saline (no reaction should be present)

Question 14

What is type 2 hypersensitivity?

Answer 14

Antibody mediated hypersensitivity
IgG (compliment system) or IgM (phagocytes) reacting with the antigen present on the surface of cells
The bound Ig interacts with complement or with Fc receptors on macrophages
Opnosisation or target cells
Immune mediated haemolysis
Takes several hours
Drug induced haemolysis

Question 15

What immunoglobulins are responsible for destroying abnormal blood

Answer 15

IgM which activates the compliment system

IgG coat blood cells and then then the FC portion will bind to antigens

Question 16

What are some examples of hypersensitivity type 2 reactions?

Answer 16

Myasthenia gravis
Graves’ disease
Pernicious anaemia
Good pasture syndrome

Question 17

Explain type 3 hypersensitivity

Answer 17

Immune Complex disease, also involves IgG
Immune complexes of antigens and antibodies form and cause damage at the site of production of circulate and cause damage elsewhere
Immune complexes take time to form and cause allergic reactions

Question 18

Give some examples of hypersensitivity type III reactions?

Answer 18

Farmers lung
Nephrotic syndrome
SLE

Question 19

Explain type 4 hypersensitivity reactions

Answer 19

Slowest form of hypersensitivity reactions that are mediated by T cells. Can take 2-3 days to develop. Delayed hypersensitivity
Macrophages present a self antigen to T cells

Question 20

Give some examples of type 4 hypersensitivity reactions

Answer 20

Rheumatoid athritis
MS
IBD
Type 1 diabetes mellitus 
Psoriasis

Question 21

How do you treat delayed hypersensitivity?

Answer 21

NSAIDS
Corticosteroids
Drugs blocking TNF and IL-6 (immune therapy)
Antibodies against B cells
Immune suppressing drugs