Type I Hypersentitivity Flashcards
What is a type I hypersensitivity reaction?
An allergy
Immunological basis for different disease.
Immediate reaction (<30mins)
Local reaction: ingested or inhaled allergen
Systemic reaction: Insect sting or IV administration
Antigens (allergens) can be environmental, non infectious antigens (proteins)
Give examples of some allergens
Seasonal exposure - Tree and grass pollen
Perennial exposure - house dust mite, Animal dander (cats and dogs), fungal spores
Accidental exposure - Insect venom (wasps / bee stings), medicines (e..g penicillin), Chemicals (latex), Foods (milk, peanuts, nuts..)
What are the mechanisms of type I hypersensitivity reactions?
Abnormal adaptive immune response against the allergens:
T helper cells cause IgE to be produced (rather than normal IgA/IgG/IgM). This IgE will the bind to mast cells and ‘sensitise them’ so that next time they come into contact with this allergen, an allergic reaction will occur.
There are different clinical allergic disorders depending on the mast cell location.
Why do westernised counties have more allergies?
Hygiene hypothesis
What things increase the risk of developing allergies?
‘Westernised’ counties Small family size Affluent, urban homes Intestinal microflora stable High antibiotic use Low or absent helminth burden Good sanitation, low orofaecal burden.
There things result in a TH2 response, causing allergic disorders. The opposite will result in a TH1 response which will be a non-allergic response.
What is the hygiene hypothesis?
Children exposed to animas, pets and microbes in the early postnatal period appear to be protected against certain allergic diseases.
What is the “old friends hypothesis” / “the biodiversity hypothesis”?
Western lifestyle induces alteration of the symbiotic relationships with parasites and bacteria leading to dysbiosis of the microbiome at the mucosal surfaces (gut).
What is Dysbiosis?
Compositional and functional alterations of microbiome
What is the microbiome?
The complete genetic content of all the microorganisms that typically inhabit in the body such as the skin or the GI tract
What is the impact of dysbiosis on human disease?
Loss of microbiotia diversity.
Caused by: Antibiotics Junkfood Urban lifestyle C section
The loss of diversity can lead to a wide variety things:
Immune diseases (IBD, MS, Coeliac, Allergy)
Obesity and T2DM
Colorectal cancer
Autism
How does allergy occur ?
IgE to mast cells - activate them / release granules.
Where do mast cels come from?
Strategic locations:
Most mucosal and epithelial tissues: GI tract, akin, respiratory epithelium
In CT surrounding blood cells.
What areas of the body contain a lot of mast cells?
Most mucosal and epithelial tissues
CT surrounding bloods cells.
List some mast cell mediators
Enzymes - tryptase - remodel CT matrix
Toxic mediators - histamine - toxic to parasites, increase vascular permeability, cause smooth muscle contraction.
Lipid mediators - Leukotrienes - SM contraction, Increase vascular permeability, stimulate mucus secretion
Lipid mediators - Platelet-activating factors - Attracts leukocytes, amplified production of lipid mediators, activates neutrophils, eosinophils and platelets
What is the immune mechanisms that leads to an allergic reaction?
- Allergen 1sr exposure (TH2 response)
- Allergen 2nd exposure (IgE cross-linking)
- Mast cell degranulation (release of granule contents and synthesis of new mediators)
