Hypersensitivity

Question 1

Type 1

Mediators
Timing
Example

Answer 1

IgE antibodies

Immediate (within 1 hour)

Anaphylaxis
Hay fever

Question 2

Type 2

Mediators
Timing
Example

Answer 2

Cytotoxic antibodies bound to cell antigens

Hours to days

Transfusion reactions
GBM disease

Question 3

Type 3

Mediators
Timing
Examples

Answer 3

Deposition of immune complexes

Typically 7-21 days

Hypersensitivity pneumatosis
Lupus

Question 4

Type 4

Mediators
Timing
Examples

Answer 4

T-cell (lymphocytes)

Days to weeks or months

TB

Question 5

Describe type 1 hypersensitivity

Answer 5

Antigen reacts with IgE bound to mast cells and basophils (in airways)

Mast cells release a form of mediator for local reactivity which act immediately

Some require degranulation or synthesis which can lead to delayed effects

Histamine predominant mediator

Question 6

What are the characteristics of type 1 sensitivity

Answer 6

Sudden onset

Skin, eyes and lips swelling

Bronchospasm

Think anaphylaxis

Question 7

Describe type 2 hypersensitivity

Answer 7

Antibodies reacting with antigenic determinants on the host cell membrane

Usually IgG or IgM

Outcome depends on where complement is activated and if metabolism of cell is affected

Question 8

Describe type 3 hypersensitivity

Answer 8

Antigen-immunoglobin complexes are formed on exposure to the allergen

Attraction causes secondary end organ inflammation

These are deposited in tissues and cause local activation of complement and neutrophil attraction

Question 9

Describe type 4 hypersensitivity

Answer 9

T-cell mediated - releases IL2 and IFy and cytokines

Requires primary sensitisation - does not happen the first time exposed to the antigen

Secondary activation takes 2-3 days to develop

May result in a normal immune reaction

If the macrophages cannot destroy pathogens they become giant cells and form granuloma

Question 10

Describe anaphylaxis

Answer 10

Type 1

Sudden onset

Systemic degranulation of mast cells and histamine release

Skin, lips and eyes swell

Bronchospasm can result in airway occlusion and death if not quickly and accurately managed

Management includes adrenaline, antihistamines, steroids

Question 11

Describe histamine

Answer 11

Regulates several essential events in immune response

Influences macrophages, dendritic cells, T lymphocytes, B lymphocytes and endothelial cells

These cells express histamine and secrete histamine - can selectively recruit major effector cells into tissue sites and affect maturation, activation, polarisation and effector function

4 histamine regulators have different effects

Question 12

What is mast cells roll in hypersensitivity reactions

Answer 12

IgE - type 1

Activation releases histamines and other mediators

Question 13

What is host cells roll in hypersensitivity reactions

Answer 13

IgG - type 2

Antigens embedded in host cells cause complement activation and destruction of MAC

Question 14

What is the role of T effector cells in hypersensitivity reactions

Answer 14

Type 4

APC activates Th1/CTL.T cells activation of macrophages and cause inflammatory response