Hypersensitivity

Question 1

Explain Hypersensitivity

Answer 1

Overreaction of the immune system.
It’s tissue damaging (immunopathologic).
There are 4 types.

Question 2

Name the environmental allergens

Answer 2

Airborne, ingested, injected and skin contact

Question 3

Describe Type I

Answer 3

Immediate allergic reaction.
Allergens trigger degranulation of mast cells and allergen specific IgE
Releases inflammatory mediators; histamine, prostaglandin etc.

Question 4

Describe Type II

Answer 4

Mediated by IgG/M antibodies.

1. Fc receptor on immunoglobulin (IgG) binds to antigen cell surface.
2. Complement cascade - complement binds to antibodies
3. Antibody dependent cellular cytotoxicity (ADCC) activated and antigen is lysed (ruptured)

Question 5

Describe Type III

Answer 5

Formed immune complexes (antigen and antibody) cause disease when lodged In tissue or blood vessels, or made in excess.
-Physiological complex normal: taken to liver and spleen and antigen killed by phagocytosis
-Pathological complex causes inflammation:
Abnormal complexes avoid phagocytosis and precipitate out into tissue and attract complement and neutrophils. Release of lysosome enzymes cause tissue damage.

Question 6

Describe Type IV

Answer 6

Cell (Th1) mediated delayed hypersensitivity
Occurs as immune system can’t destroy environmental agents.
Activation of T cells, cytokines and macrophages causes tissue destruction which may be permanent

Question 7

Define atopy

Answer 7

Production of IgE to normal, common environmental allergens

Question 8

What is a hapten

Answer 8

Occurs in Type IV
When non-infectious antigens (too small to produce immune response) bind to host proteins to produce antigenic stimulus to induce response and host protein is a Carrier.

Question 9

Define autoimmune disease

Answer 9

Where the body produces antibodies that attack its own tissue, destroying it.

Question 10

Types of immunological tolerance

Answer 10

Central Tolerance - maturing B and T cell and rendered non-reactive to self
Peripheral tolerance - After maturation of T & B cells. Inhibiting auto-reactive cells which escape the central tolerance process

Question 11

Aetiology factors of autoimmune disease

Answer 11

Genetic factor - susceptibility to develop disease
Immune regulatory factors - defective tolerance
Hormones
Environmental - infectious and environmental agents

Question 12

Autoimmune disease mechanism

Answer 12

1. initiating event - infection
2. genetic factor - susceptibility
3. breakdown of self tolerance
4. auto-reactivity - own antibody production and activation of complement
5. Immune complex formation
6. Recruitment of immune defence causing tissue damage

Question 13

Difference between organ-specific and non-organ specific autoimmune disease

Answer 13

O-S: immune response direct against antigen in single organ

N-O S: response directed against self-antigens present in many organs and tissue causing widespread tissue damage

Question 14

What is serum sickness?

Answer 14

In type 3 - Systemic illness where immune complexes are deposited throughout many tissues

Question 15

What is Arthus reaction?

Answer 15

In type 3 - localised disorder where the complexes form locally in the tissue