Hypersensitivities

Question 1

Type I hypersensitivity reactions are mediated by

Answer 1

IgE and results from the actions of mediators by mast cells

Question 2

Type II hypersensitivity reactions are mediated by

Answer 2

Abs that bind tissue Ags and cause complement dependent tissue injury and disease

Question 3

Type III hypersensitivity reactions are mediated by

Answer 3

Circulating Ag-Ab complexes which deposit in vessels and cause complement dependent injury in the vessel wall (vasculitis)

Question 4

Type IV hypersensitivity reactions are mediated by

Answer 4

T cells and results from inflammation caused by cytokines produced by CD4+ Th1 and Th17 cells, macrophages, or killing of host cells by CD8+ CTLs

Question 5

What happens in the initial allergen encounter in type I hypersensitivity reactions?

Answer 5

Th2 and IL-4

Adaptive immune response by B cells that mature into plasma cells to make IgE to that allergen

Question 6

What unique property does IgE have?

Answer 6

It enters the circulation and is rapidly bound by FcRe (CD23) on mast cells in the tissues

Question 7

What occurs during the subsequent allergen encounter during a type I hypersensitivity reaction?

Answer 7

Cross linking causes mast cell degranulation that releases vasoactive amines, cytokines/chemokines and lipids

Question 8

What are the important mediators of type I hypersensitivity reactions?

Answer 8

Histamine, proteases, prostaglandins, leukotrienes and cytokines

Question 9

What role does histamine play during type I hypersensitivity reactions?

Answer 9

The major amine that causes dilation of small vessels and increases vascular permeability

Question 10

What role do proteases play during type I reactions?

Answer 10

May cause local tissue damage

Question 11

What role do prostaglandins have during type I reactions?

Answer 11

Cause vascular dilation

Question 12

What role do leukotrienes play in type I reactions?

Answer 12

Stimulate prolonged smooth muscle contraction

Question 13

Describe immediate phase of type I reactions

Answer 13

Characterized by vasodilation, congestion and edema

Question 14

Describe the late phase of type I reactions

Answer 14

Develops 2-24 hours later

Characterized by an inflammatory rich in eosinophils, neutrophils and T cells

Question 15

What are the aims of allergen SIT?

Answer 15

To induce peripheral T cell tolerance to allergens
To increase the thresholds for mast cell and basophil activation by allergens
To decrease IgE mediated histamine released by mast cells

Question 16

What is penicillin induced anemia?

Answer 16

Type II hypersensitivity reaction
The drug binds directly to the RBC surface and induces an anti drug Ab
These conditions improve when the drug is discontinued

Question 17

Describe Quinidine induced anemia

Answer 17

Type II hypersensitivity reaction
Auto Abs form immune complexes with the drug
The ICs can bind to the erythrocyte surface through CR1
Tx may require immunosuppression and/or plasmapheresis to remove the ICs

Question 18

Describe methyldopa induced anemia

Answer 18

Type II hypersensitivity reaction
This drug induces an anti drug Ab that cross reacts with an Rh Ag
Tx may require immunosuppression and/or plasmapheresis to remove the auto Abs

Question 19

List type II hypersensitivity reaction diseases

Answer 19

Autoimmune hemolytic anemia, autoimmune thrombocytopenic purpura, goodpasture’s syndrome, Grave’s disease (hyperthyroidism), Myasthenia gravis, pemphigus vulgaris, pernicious anemia and rheumatic fever

Question 20

What is hemolytic disease of newborn?

Answer 20

During delivery of the first pregnancy, Rh antigens enter the mother’s circulation through breaks in the placenta -> mother makes anti-Rh Abs -> mother has anti-Rh Abs -> anti-Rh Abs cross the placenta and destroy fetal blood cells of the subsequent pregnancy

Question 21

How can HDN be prevented?

Answer 21

By immunotherapy with anti-(anti-Rh) at around week 28 of pregnancy

Question 22

Which diseases are associated with type III hypersensitivity reactions?

Answer 22

SLE, polyarteritis nodosa, post-streptococcal glomerulonephritis, serum sickness, arthus reaction

Question 23

What causes the tissue injury seen in type IV hypersensitivity reactions?

Answer 23

Caused by inflammation induced by cytokines that are produced mainly by CD4+ T cells (Th1 and Th17 cells), macrophages and/or by killing of host cells by CD8+ CTLs

Question 24

Autoimmune disease mediated by type IV hypersensitivity reactions include

Answer 24

Multiple sclerosis, rheumatoid arthritis and type 1 DM

Question 25

Inflammatory disease with a microbial component associated with type IV hypersensitivity reactions

Answer 25

Crohn’s disease (IBD) is likely caused by the aberrant reactions to intestine microflora which have an autoimmunity component
The other diseases like tuberculosis are caused by reactions to microbial Ags