Hypersensitivity

Question 1

What is hypersensitivity?

Answer 1

A group of disorders where the normally beneficial components of the immune system response act in an exaggerated or inappropriate fashion to environmental antigens which do not normally cause tissue damage. The exaggerated response directed at antigen rather than the antigen itself is responsible for the tissue damage which results

Question 2

What does ACID stand for in the types of hypersensitivity?

Answer 2

A = anaphylaxis
C = cytotoxic 
I = immune complex 
D = delayed

Question 3

Pathology of Type I hypersensitivity reaction

Answer 3

ALLERGY
Most allergies IgE mediated
Genetically hypersensitive TH cells
Immediate reaction

Question 4

Phases of type I hypersensitivity reaction

Answer 4

Sensitisation phase
Reaction phase (early and late)

Question 5

Treatment of type I hypersensitivity reaction

Answer 5

Antihistamines
Corticosteriods
Adrenaline
Allergen avoidance

Question 6

Pathology of Type II hypersensitivity

Answer 6

BLOOD TYPES
Cytotoxic
Coombs test

Question 7

Pathology of type III hypersensitivity

Answer 7

COMPLEXES
Antigen antibody / immune complex formation
Deposition in tissues
Activating phagocytes and causing damage
Complexes form from fragments but are too small for macrophages to sweep up
They deposit in tissues where in complement is activated - causing INFLAMMATION

Question 8

Example of a condition which involves type III hypersensitivity and its pathology

Answer 8

SLE

• failure of tolerance, allowing “self reactive” B/T cells to circulate
• Leaked auto antigen is presented to B cell, passed to T helper cells and antibodies to DNA made

Question 9

Pathology of Type IV hypersensivity reaction

Answer 9

DELAYED
T cell mediated = cytotoxic (CD8+) and helper (CD4+)
Tc cells themselves can attach MHC1 APCs
They release perforin to damage cell surface

Question 10

What type of hypersensitive is the most direct form of reaction?

Answer 10

Type IV (delayed)

Question 11

What is atopy?

Answer 11

Genetic tendency to develop allergic diseases

Question 12

What is atopic dermatitis?

Answer 12

Eczema

Question 13

Who is atopic dermatitis common in?

Answer 13

Children

Question 14

Pathology of atopic dermatitis

Answer 14

Degranulation of basophils and mast cells in response to sensitised IgE
“Leaky” skin allows more allergen in and water out

Question 15

Presentation of atopic dermatitis

Answer 15

Exposed and flexor surfaces

Dry and itchy

Question 16

Pathology of contact dermatitis

Answer 16

Langerhans cells present to TH1 cells
TNF alfa and IL 1, 13 and 18
LCs become differentiated dendritic cells presenting allergenic epitope and multiply

Question 17

When is there a more aggressive response of contact dermatitis?

Answer 17

2nd time

Question 18

What does a type I hypersensitivity reaction lead to?

Answer 18

Rapid and later smooth muscle contraction
Bronchoconstriction
Inflammation

Question 19

How often does type IV hypersensitivity take to react to a pathogen?

Answer 19

Up to 48 hours