Immunopathology - Week 7 - Hypersensitivity reactions and disorders

Question 1

What are Hypersensitivity reactions?

Answer 1

Hypersensitivity reactions= exaggerated/unwan ed immune responses
that can cause serious cell/tissue injury.

Question 2

List the 4 types of hypersensitivity reactions.

Answer 2

Type 1: Anaphylactic reactions.
Type 2: Tissue specific reactions.
Type 3: Immune complex reactions.
Type 4: Delayed Hypersensitivity reactions.

Question 3

Describe the mechanisms that exert the effect of an type 1 anaphylactic reaction.

Answer 3

Associated with parenteral administration of protein antigens. Such as, bee venom, drugs and some food.

Within minutes of exposure, itching, hives and skin erythema appear.
- Dyspnoea (breathlessness)
- Laryngeal oedema may cause obstruction of the upper airway
- Shock

Question 4

Provide examples of disorders caused by type 1 anaphylactic reactions.

Answer 4

• Insect sting anaphylaxis
• Drug-induced anaphylaxis
• Food allergy - induced anaphylaxis

Question 5

Describe the mechanisms that exert the effect of an type 2 Tissue specific reactions.

Answer 5

Mechanism 1:
Antibody attaches to either a tissue specific antigen or to an antigen which attaches to the tissue.
Complement enzymes attach to this combination and destroy the cells.

Mechanism 2:
Antibody attaches to either a tissue specific antigen or to an antigen which attaches to the tissue.
- Phagocytosis

Mechanism 3:
Neutrophils are attracted and attempt to phagocytose, but cannot always do so due to size of the tissue—they release enzymes to damage the tissue.

Mechanism 4:
The antibody is recognised by receptors on
Natural Killer cells
which then releases toxic substances which cause damage to the tissue.

Mechanism 5:
The effect of the antibody binding with the target cells causes an alteration in function, rather than destroying the
tissue.

Question 6

Provide examples of disorders caused by type 2 Tissue specific reactions.

Answer 6

• Graves disease
• Transfusion reaction.

Question 7

Describe the mechanisms that exert the effect of an type 3 Immune complex reactions.

Answer 7

The antigen and antibody join and form a complex prior to depositing on innocent tissue.

Question 8

Provide examples of disorders caused by type 3 Immune complex reactions.

Answer 8

Extrinsic allergic alveolitis:
Develops in response to repeated inhalation of antigenic materials from moulds, plants or animals.

Acute poststreptococcal glomerulonephritis:
Caused by antibodies which are formed in
response to the streptococcal. It damages the kidneys.

Rheumatoid arthritis
Systemic lupus erythematosus

Question 9

Describe the mechanisms that exert the effect of an type 4 Delayed Hypersensitivity reactions.

Answer 9

Is mediated by specifically sensitised T lymphocytes and does not involve antibodies.

Tc cells directly damage target tissue by releasing toxins.

Question 10

Provide examples of disorders caused by type 4 Delayed Hypersensitivity reactions.

Answer 10

• A positive Mantoux reaction.
• Allergic contact dermatitis.

Question 11

Explain the relationship between hypersensitivity reactions, autoimmunity and allergic reactions.

Answer 11

Hypersensitivity attacks itself or external things, Autoimmunity attacks itself and Allergy attacks external things.

Hypersensitivity is a exaggerated immune response, Autoimmunity is a reaction against self-antigens, Allergy is a reaction against harmless environmental antigens.

All three use hypersensitivity types.

Question 12

Briefly explain the broad mechanisms underlying graft rejection.

Answer 12

Graft rejection occurs when the host recognizes the
grafted tissue as foreign.
There are three types of Graft rejection.
1. Hyperacute rejection
2. Acute rejection
3. Chronic rejection