Hypersensitivity

Question 1

Hypersensitivity types

Answer 1

• type 1: anaphylaxis
• type 2: Ab mediated within blood
• type 3: clumping of Ab/Ag
• type 4: cell-mediated, delayed hypersensitivity

Question 2

Type 1 HSR,
mech,
timeline of events

Answer 2

• cross linking of IgE on mast cells by antigen causes release of histamine (immediate rxn)
• Delayed rxn: 6 hours later, continued swelling from leukotrienes, which cause acute inflammation (influx of neutrophils, etc)

Question 3

Asthma airway hyperactivity is caused by what cytokine

Answer 3

-IL13

Question 4

“hygiene” hypothesis of type I HSR prevalence

Answer 4

• IgE evolved to combat parasites, and in most of the world IgE is used up to fight them
• However, in the developed world, IgE is available to cause allergic reactions

Question 5

What cytokine is increased in Type I HSR?

Answer 5

• IL4

- used to induce class switching of B Cells to IgE

Question 6

Type I HSR: why treat by injecting antigen regularly?

Answer 6

• this allows the IgE to be used up gradually

- dangerous reactions occur because IgE builds up to high levels and is then used up

Question 7

Type 2 HSR, mech

Answer 7

-Ab reacts with antigen, then recruits complement to attach cell

Question 8

Type 3 HSR, mech

Answer 8

• Ab/Ag complexes are formed, which clump and be deposited in tissues, then recruit complement
• deposited esp in joints, kidney, and vessels
• Arthus reaction
• Serum sickness

Question 9

Arthus reaction

Answer 9

• type 3 HSR

- inflammation caused by local deposition of Ab/Ag complexes

Question 10

Serum sickness

-timeline

Answer 10

• type 3 HSR
• can occur with serum of other animals
• systemic inflammatory response to presence of immune complexes deposited in many areas of the body.
• occurs 7-10 days after antigen exposure because this is time for IgM to switch to IgG
• ex: penicillin allergy

Question 11

Type 4 HSR, mech, examples

Answer 11

• T cell-mediated, delayed hypersensitivity
• can be CD8 cell mediated, or CD4/macrophage mediated.
• no Ab
• starts hours/days after contact with antigen, can last for days
• Ex: contact dermatitis from poison oak (CD8 cells)
• Ex: Tuberculin skin test (CD4/macrophages)

Question 12

Tuberculin test

Answer 12

• type 4 HSR, delayed hypersensitivity

- rash caused by CD4, macrophages

Question 13

What mediator is released within 15 minutes of anaphylaxis and is used to identify mast cell release?

Answer 13

Tryptase

Question 14

Cytokine mediators released by mast cell in Type 1 hypersensitivity

• when released?
• list them

Answer 14

• 4-6 hours after degranulation
• IL4, IL13
• IL3, IL5, GM-CSF
• TNF

Question 15

RANTES (CCL5), Eotaxin (CCL11)

Answer 15

chemokines released by mast cells, chemotactic for T cells and eosinophils

Question 16

Why are steroids a tx for Type 1 hypersensivity?

Answer 16

• steroids induce apoptosis of eosinophils

- reduce IL5 production

Question 17

IL5

• produced why who
• what does it do

Answer 17

• produced by Th2 cell
• prolongs survival of eosinophils
• enhances cytoxicity against parasites

Question 18

why can’t you do a skin allergy test (type 1) immediately after an anaphylactic event?

Answer 18

-IgE all used up. wait 4-6 weeks, otherwise get false negative.

Question 19

Farmer’s lung

Answer 19

type 3 HSD due to Ab against hay dust or mold spores

-affects alveolar wall

Question 20

Type 4 HSD: how long does it take to occur?

Answer 20

24-72 hours to develop