Hypersensitivity Response

Question 1

Define hypersensitivity

Answer 1

An exaggerated or inappropriate adaptive immune response to an antigen/ immunogen, causing tissue damage.

Question 2

What are the four types of hypersensitivity reactions?

Answer 2

Type l: immediate, IgE antibody is the mediator (e.g. hay fever)
Type ll: cytotoxic, IgG & IgM antibody. (eg. Transfusion)
Type lll: complex mediated, IgG & IgM antibodies. (eg. farmer’s lung)
Type lV: delayed, T lymphocyte & macrophages are the mediators. (eg. Contact dermitis)

Question 3

Define Type l hypersensitivity

Answer 3

Immediate reaction. Immunogen referred to as allergen. Reactions due to specific triggering of IgE-sensitised mast cells. Leads to release of pharmacological mediators of inflammation.

Question 4

What is Anaphylaxis?

Answer 4

Generalised type l reaction, leading to vasodilation and constriction of bronchial smooth muscle. Can result in death.

Question 5

What is the genetic predisposition to produce IgE? (Type l)

Answer 5

Atopy

Question 6

Describe the sequence of events relating to a type l reaction.

Answer 6

1) allergen absorbed through mucosa
2) APC presents processed allergen
3) B cells produce specific IgE with T cell help
4) Allergen specific IgE binds to mast cell via Fc receptors.
5) Allergen cross-links surface bound IgE
6) Mast cell degranulation.

Question 7

What are the mast cell granules?

Answer 7

Histamine- causes smooth muscle contraction, vasodilation and increased mucus secretion.
Eosinophil chemotactic factor- attracts eosinophils from inflamed blood vessels.
Neutrophil chemotactic factor.

Question 8

What are the secondary mediators for type l reaction?

Answer 8

Leukotrienes- cause prolonged contraction of smooth muscle.
Prostaglandins- causes vasodilation, smooth muscle contraction.
Secondary are formed fro membrane phospholipids when IgE is cross linked at mast cell surface.

Question 9

What are the consequences of a Type l reaction?

Answer 9

Anaphylactic shock- due to systemic release of mast cell mediators.
Hay fever
Allergic Asthma
Food allergies

Question 10

Define Type ll hypersensitivity

Answer 10

Cytotoxic hypersensitivity.
Antibodies directed against antigen on surface of specific cells or tissues. Involves IgM and IgG antibodies. They interact with complement components and immune cells.

Question 11

What are the consequences of antibody binding to antigen? (Type ll)

Answer 11

Cell lysis
Deposition of complement components
Macrophage & neutrophil activation

Question 12

What are some examples of type ll hypersensitivity?

Answer 12

Blood transfusion
Hyperacute graft rejection
haemolytic disease of the newborn
reactions to tissue antigens.

Question 13

What is HDN?

Answer 13

Haemolytic Disease of the Newborn.
IgG antibodies pass through placenta. Some attack RBC of foetus, breaking down and destroying cells.
Due to Rhesus incompatibility.

Question 14

What are the effects of anti-Rh antibodies?

Answer 14

spontaneous abortion
baby born with mild jaundice
baby born with HDN

Question 15

How can anti-Rh antibodies effects be prevented?

Answer 15

Treat mother with anti-Rh antibodies within 72 hours of birth of each Rh+ child.

Question 16

How can HDN be treated?

Answer 16

careful monitoring of Anti-Rh antibodies in mother; exchange transfusion of newborn.

Question 17

Define Type lll hypersensitivity

Answer 17

Antibodies directed against soluble antigens in serum. Can also be directed against widely distributed antigen. Deposits of complexes can damage organs.
Also known as immune complex hyper.

Question 18

What are examples of type lll hypersensitivity?

Answer 18

Persistent Infection- antibodies formed against microbial antigens.
Autoimmunity- antibodies formed against self antigens.

Question 19

What is intrinsic allergic alveolitis?

Answer 19

Occupational disease due to inhalation of immunogenic proteins or spores. e.g. farmer’s lung. Mushroom, coffee, cheese workers disease.

Question 20

What’s farmers lung?

Answer 20

Starts with mild cough in Winter.
Leads to emphysema
years of exposure = high levels of IgG to spore antigens. Complexes precipitate in lung.

Question 21

What is serum sickness?

Answer 21

occurs following treatment of an active infection with antibodies.
weakness, joint pains, fever, skin rash, oedema.

Question 22

Define type IV hypersensitivity

Answer 22

Called DTH (delayed type hyper reaction)
takes >12 hours to develop. Mediated by T lymphocytes & macrophages.