Type 1 Hypersensitivity Flashcards
What is a hypersensitivity reaction?
An exaggerated immune response against an antigen that can cause damage
What is autoimmunity?
When the hypersensitivity reaction is against a self antigen
What is a hapten?
A small molecule that can bind to a protein and stimulates antibody production.
What is an example of a hapten?
Penicillin.
What is a cytokine storm?
When the immune response causes damage and this damage is greater than the benefit. They recruit pro inflammatory cells and can cause a systemic response.
What is type 1 hypersensitivity also known as?
Allergy
Atopy
What is a type 1 hypersensitivity reaction?
An immediate hypersensitivity to environmental antigens.
What type of antigens cause type 1 hypersensitivity reaction?
Environmental antigens only. Food mould drugs medications pollen bee stings latex lotions soaps
Which antibody is most common in type 1 hypersensitivity reaction?
IgE
What is the pathophysiology behind type 1 hypersensitivity reactions?
- Antigen enters the Body
- Th2 (T helper cells 2) secrete IL4 (a cytokine)
- This causes B cells to produce IgE antibodies and turns off Th1 cells
- Mast cells attach themselves to IgE antibodies and eosinophils also migrate towards the hypersensitivity reaction
- Mast cells and eosinophil cells degranulate and release histamine, prostaglandins and leukotrienes
- This causes an immune response - smooth muscle contraction, blood vessel dilation, oedema, hives
What is the difference between Th1 and Th2?
Th1 - gives an immune response against intracellular parasites
Th2- gives an immune response against extracellular parasites
How are type 1 hypersensitivity reactions mediated?
Through the degranulation of mast cells and eosinophils
How long do type 1 hypersensitivity reactions take to feel effects?
Within seconds - its immediate
What are allergens?
External antigens which cause an allergic reaction
what is someone specifically allergic to in a penicillin allergy?
Beta lactam
Which exposure to an allergen is most serious?
The second - after IgE antibodies have been created.
When do late phase allergic reactions occur?
8-12hrs after exposure
What is the role of cytokines?
They excite T cells (Th2) which in turn excite B cells to produce IgE antibodies specific to the antigen
What are known genetic predispositions for type 1 hypersensitivity reactions?
Change in filaggrin
Increased Th2
When does an immediate allergic response occur?
The 2nd encounter to the antigen, once IgE antibodies have been produced
What happens during anaphylaxis?
Airways constrict Increased vascular permeability Low blood pressure Angioedema Shift of fluid from intravascular to extravascular space
What are common types of type 1 hypersensitivity reaction?
Anaphylaxis Asthma Rhinitis Urticaria Angioedema Atopic eczema Dermatitis Hives
What is an allergic march?
When you develop an allergy young you’re more likely to develop more as you age.
What is the pathophysiology behind allergic rhinitis?
Mast cells degranulate and cause nasal stuffiness and sneezing
Leukotrines increase mucus section = runny nose
What is the pathophysiology behind asthma?
Leukotrines cause smooth muscle contraction
What are the treatments for type 1 hypersensitivity reactions?
Desensitisation Beta 2 adrenergic agonists Epinephrine Antihistamines Montelukast
What do beta 2 adrenergic agonists do?
Example - salbutamol
prevent smooth muscle contraction in the chest
What does epinephrine do?
Its life saving in anaphylaxis
Stimulates alpha and beta adrenergic receptors which decrease vascular permeability, increase blood pressure and reverse airway obstruction
What do antihistamines do?
Block histamine receptors
Good for skin, nose and mucus allergens
Doesn’t work in asthma (not caused by histamine release)
How does montelukast work>
Its a specific receptor antagonist that blocks the effect of leukotrienes
Which 3 things are released by mast cell degranulation?
Histamine
Leukotrienes
Prostaglandins
How do corticosteroids work?
Prevent the hypersensitivity reaction.
