Immunopathology - Hypersensitivity Flashcards
What is the definition of allergy?
a reaction produced by the normal immune system in a pre-sensitized (immune) host
What type of antigens are involved in allergy?
the normal immune response is directed against innocuous antigens
these are harmless antigens
How did Coombs & Gell classify hypersensitivity?
There are 4 types of hypersensitivity reactions
What is the role of a dendritic cell?
they are APCs that process antigens and present them to T cells
they are messengers between the innate and adaptive immune systems
What characterises a Type 1 hypersensitivity reaction?
IgE antibodies initially sensitize individuals to an antigen
They provoke a quick inflammatory response upon subsequent exposures
What is meant by ‘immunopathogenesis’?
the process of disease development involving an immune response or components thereof
What are the 2 stages involved in the immunopathogenesis of Type 1 hypersensitivity reactions?
- IgE antibody mediated mast cell and basophil degranulation
- release of preformed and de novo synthesised inflammatory mediators
What are the 2 main clinical features of a Type 1 hypersensitivity reaction?
- fast onset - 15-30 mins
2. weal and flare
What types of cells are involved in the late phase response of a Type 1 hypersensitivity reaction?
- eosinophils
2. Th2 T cell
What happens in a Type 1 hypersensitivity reaction when antigen comes into contact with a mast cell?
The antigen bound to IgE cross-links with membrane-bound IgE antibodies on the mast cell membrane
What is involved in the primary response of a Type 1 hypersensitivity reaction?
The mast cell degranulates and releases
- Histamine
- proteases
- chemotactic factors
What are chemotactic factors?
Substances that stimulate cellular migration (chemotaxis)
What is involved in the secondary response of a Type 1 hypersensitivity reaction?
reaction of the antigen with IgE on mast cells causes the
synthesis and release of:
- prostaglandins
- leukotrienes
What is the role of histamine that is released in a Type 1 hypersensitivity reaction?
- blood clots
- gastric acid secretion
- dilation of blood vessels
- bronchoconstriction
- increases capillary permeability
- adrenaline release
- swelling and inflammation
- increases heart beat frequency
What is the role of Th2 cells in Type 1 hypersensitivity reactions?
- antigen is taken up by a dendritic cell and presented on a class II MHC molecule
- This is recognised by the Th2 cell
- Th2 cells produce cytokines which stimulate proliferation of IgE producing plasma cells
What is meant by the mast cell being ‘sensitised’?
It has IgE molecules, attached via their constant region, on its membrane
What happens when someone is exposed to an antigen for a second time in a T1 HS reaction?
The antigen binds to IgE attached to the mast cells and causes degranulation
2 IgE molecules must react with the specific antigen
What is the definition of anaphylaxis?
an acute, potentially life-threatening IgE mediated systemic hypersensitivity reaction
What are the symptoms of a mild Type 1 hypersensitivity reaction?
- itchy eyes or nose
- cutaneuous pruritus
- flushing
- urticaria
- oral tingling/pruritus
- abdominal pain/nausea/vomining
- runny nose and sneezing
What is cutaneous pruritius?
Itchy skin
It is an unpleasant sensation of the skin that provokes the urge to scratch
What is urticaria?
“Hives” is an outbreak of swollen, pale red bumps or plaques (wheals) that appear suddenly on the skin
What is another way of describing a moderate-severe type 1 hypersensitivity reaction?
anaphylaxis
What are the symptoms of anaphylaxis related to the skin and pain?
- diffuse urticaria
- angioedema
- severe abdominal pain and vomiting/diarrhoea
What are the symptoms of anaphylaxis relating to the lungs and breathing?
- hoarseness and cough
- shortness of breath
- wheezing and cyanosis - can lead to respiratory arrest