Type 1 hypersensitivity Flashcards
What is type 1 hypersensitivity?
IgE dependent allergic hypersensitivity (Anaphylactic)
What is type 1 hypersensitivity mediated by?
Mast cells, basophils, IgE and allergens
What is an allergen?
Substance that when ingested the immune system recognises as foreign and causes an allergic reaction.
What does antigenic mean?
Any substance usually a foreign substance capable of evoking an immune response
What is an antigen
Usually a foreign substance, such as a toxin a component of a virus, bacterium, or parasite.
What are the products of an immune response?
T-cells
Antibodies
What is immunological hypersensitivity?
undesirable reactions produced by the normal immune system, including allergies
What is the first step in the immune response?
Sensitisation
What is the role of antigen presenting cells?
They stimulate the activation of auto-reactive T or B cells
They process and express the allergens on their cell surface
Where are mast cells?
(Tissue-dwelling)
What is the importance of mast cells?
They contained pre-formed mediators such as; histamine, heparin and proteases
How mast cells activated?
By the cross-linkage of cell bound IgE
By IgE Independent mechanisms
Innate immune mechanisms
What stages are mast cells involved in?
Early and late inflammatory events
Where are mast cells derived?
From bone marrow
What is the role of IL-4 and IL-13?
Promotes Th2 and IgE production
What is the first step in the Development of allergic sensitisation?
Detection of the allergen by dendritic antigen presenting cells
What happens after an allergen is detected?
The APC interacts with naive T lymphocytes cells by ligation of MHC II molecules on the APC by T cell receptors.
What happens in the allergen development once the dendritic cell has interacted with a naive T cell?
In the presence of IL-4 the Naive T-cell switches phenotype to TH2
TH2 reacts with naive B cells in the presence of IL-4 and IL-13
What happens after this?
B-cells switch to antibody production of IgE
What is an important feature of B-cells and T-cells?
They have immunological memory.
In the presence of the allergen it will cause expansion and production of the allergen specific IgE
What is the role of TNF-alpha?
Promotes tissue inflammation
What are Basophils?
Type of WBC, that circulate the body
What do basophils contain?
Histamine and other pre-formed mediators
What is the main role of basophils?
They migrate to sites of allergic inflammation.
What is the indication of a low basophil level?
A severe allergic reaction
How are basophils activated?
Via pathogen associated molecular patterns.
What is the most common inflammatory mediator and what is its role?
Histamine - it triggers vasodilation and increases vascular permeability
What is IgE cross-linking and what does it cause?
IgE molecules cross linking leading to intracellular signalling.
