1.2.1 Type I Hypersensitivity Reactions Flashcards
What is a type 1 hypersensitivity reaction?
Allergy
What are the 3 features of type 1 HSRs?
Immunological basis for different diseases
-Different organs affected
Immediate reaction
-Local reaction: ingested or inhaled allergen
-Systemic reaction: insect sting or IV administration
Antigens
-Allergens, environmental, non-infectious antigens (proteins)
What are the 3 different types of allergen exposure?
Seasonal
Perennial
Accidental
Give an example of a seasonal allergen exposure
Tree and grass pollens
Give examples of perennial allergen exposures
House dust mite
Animal dander- cats and dogs
Fungal spores
Give examples of accidental exposure allergens
Insect venom- wasp and bee stings
Medicines- penicillin
Chemicals- latex
Foods- milk, peanuts, nuts, shellfish etc.
What is a cross reaction?
Foods/substances which have a similar structure to something that you are allergic to, which will cause you to have an allergic reaction
What are the two mechanisms of T1HSRs?
Abnormal adaptive immune response against the allergens
Mast cell activation
Outline the abnormal adaptive immune response against allergens mechanism
T helper 2 (TH2) response (IL,4,5 and 13)
IgE production
Outline the mast cell activation mechanism
Sensitised individuals
Different clinical allergic disorders depending on location of mast cell
Why are people with westernised lifestyles more susceptible to allergies?
Due to less exposure to allergens
What is the hygiene hypothesis?
Children exposed to animals, pets and microbes in the early postnatal period appear to be protected against certain allergic diseases
What is microbial dysbiosis?
Alteration of the symbiotic relationships with parasites and bacteria causing compositional and functional alterations of the microbiome
Associated with western lifestyle due to reduced exposure to bacteria
What is the impact of microbial dysbiosis on diseases?
Increased:
- Immune diseases
- Metabolic diseases
- Autism
- Colorectal cancer
What two ways can mast cells become activated?
IgE- dependent mechanism
Non-IgE dependent mechanism
What is the strategic location of mast cells?
Most mucosal and epithelial tissues
e.g. GI tract, skin, respiratory epithelium
Connective tissue surrounding blood cells
What is the role of mast cells?
- Activation of effector cells- T cells, neutrophils etc.
- Direct antimicrobial effect
- Recruitment of effector cells
- Physiological tissue remodelling e.g. pregnancy
- Angiogenesis regulation- formation of blood vessels
What are the 4 main mast cell mediators?
Tryptase
-Enzyme
Histamine
-Toxic mediator
Leukotrienes C4,D4,E4
-Lipid mediator
Platelet-activating factor
-Lipid mediator
What is the biological effect of tryptase?
Enzyme class
Remodels connective tissue matrix
What is the biological effect of histamine?
Toxic mediator class
Toxic to parasites
Increases vascular permeability
Causes smooth muscle contraction
What are the biological effects of leukotrienes C4,D4 and E4?
Lipid mediator class
Cause smooth muscle contraction
Increases vascular permeability
Stimulates mucus secretion
What is the biological effect of platelet-activating factor?
Lipid mediator class
Cause smooth muscle contraction
Increases vascular permeability
Stimulates mucus secretion
