Allergy

Question 1

What is allergy and hypersensitivity?

Answer 1

Undesirable, damaging, discomfort-producing and sometimes fatal reactions produced by the normal immune system (directed against innocuous antigens) in a pre-sensitized (immune) host.

Question 2

What are the two immunopathological classifications?

Answer 2

Coombs & Gell 1963- IV types

Extended classification- type V

Question 3

What is the immunopathogenesis of type ii cytotoxic reactions?

Answer 3

IgG/IgM Ab response against combined self/foreign antigen at the cell surface- complement activation/phagocytosis/ADCC

Question 4

What are the clinical features of type ii cytotoxic reactions?

Answer 4

Onset minutes to hours

Cell lysis and necrosis

Question 5

What are the common antigens of type ii cytotoxic reactions?

Answer 5

Penicillin

Question 6

What are the associated diseases of type ii cytotoxic reactions?

Answer 6

Erythroblastosis fetalis,

Goodpasture’s nephritis

Question 7

What is the immunopathology of type iii immune complex?

Answer 7

IgG/IgM Ab against soluble antigen- immune complex deposition

Question 8

What are the clinical features of type iii immune complex?

Answer 8

Onset 3-8h

Vasculitis

Question 9

What are the associated diseases of type iii immune complex?

Answer 9

SLE

Question 10

What is the traditional cause of type iii immune complex?

Answer 10

serum sickness

Question 11

What is the immunopathology of type IV delayed hypersensitivity?

Answer 11

Antigen specific T-cell mediated cytotoxicity

Question 12

What are the clinical features of type IV delayed hypersensitivity?

Answer 12

Delayed onset 48-72h

Erythema induration

Question 13

What is the common antigen of type IV delayed hypersensitivity?

Answer 13

Metals-e.g nickel

tuberculin reaction

Question 14

What is the associated disease of type IV delayed hypersensitivity?

Answer 14

Contact dermatitis

Question 15

Why do we get allergies?

Answer 15

Those components of the immune system involved in responses to parasitic infection are also involved in allergic responses

The system has developed to produce a rapid tissue-based response to re-infection

The lack of infectious drive (fewer infections) is a contributory factor in allergic disease

Question 16

What is the immune response to parasitic disease?

Answer 16

Increased levels of IgE
- Total
- Specific to pathogen – cross-reactive
Tissue inflammation with:
- eosinophilia & mastocytosis
- Basophil infiltration
Presence of CD4+ T cells secreting:
- IL4, IL5 & IL13

Question 17

What is the hygiene hypothesis?

Answer 17

Stimulation by microbes is protective

Question 18

What are the genetic influences on the allergic immune response?

Answer 18

Polygenic diseases
Cytokine gene cluster IL3,5,9,13
IL12R; IL4R
FcεRI
IFNγ; TNF

Question 19

Are genetic influences sufficient for disease?

Answer 19

NOT sufficient for disease

ONLY susceptibility

Question 20

What are allergens?

Answer 20

Antigens that initiate an IgE-mediated response

First encounter results in innate & IgM response

Question 21

What happens in a conventional immune response?

Answer 21

Allergen requires processing
Presentation to T cells & cytokine release
Results in delineation of T-helper subsets into different types

Question 22

What is the immunopathogenesis of an IgE mediated allergic response?

Answer 22

IgE Ab mediated mast cell and basophil degranulation- release of preformed and de novo synthesized inflammatory mediators

Question 23

What are the clinical features of an IgE mediated allergic response?

Answer 23

Fast onset (15-30 min)
Wheal and flare