2 Hypersensitivity Type 1 Flashcards
A patient is stung by a bee and develops an allergic reaction. How might the patient present?
Wheezing
Difficulty breathing
Light headed
Altered conciousness
Low BP
Swollen face
Generalised skin rash
What cell types are involved in type I hypersensitivity reactions? (2)
Type 1 hypersensitivity= an allergy
- IgE
- Mast cells
Give some examples of allergens.
Allergen=antigen causing a reaction
(Think seasonal exposure, perennial (lasting or existing for a long or apparently infinite time) exposure, accidental exposure)
- Pollens
(allergens= usually proteins)
- Houst dust mite
- Animal dander
- Fungal spores
- Insect venom
- Medicines eg penicillin
- Chemicals eg latex
- Foods eg milk, peanuts
Why do allergies tend to run in families?
Allergies- genetic predispostion
T-helper cells= hypersensitive
TH2 cells also stimulate degranulation of eosinophils
Outline how sensitisation occurs.
IgE produced by B-cell (which was activated by hypersensitive T-helper cell) activate mast cells
Mast cells now ‘sensitised’
How do we treat type 1 hypersensitivity reactions?
What is the ‘hygiene hypothesis’? (with relation to type 1 hypersensitivty reactions)
What is the ‘old friend hypothesis’ with relation to allergies?
eg people who are delivered via C-section 8x more liekly to develop an allergy
Where in the body do we find mast cells?
- Most mucosal and epithelial tissue
- In connective tissue surrounding blood vessels
- Produce by bone marrow- mature in tissues
- Activated near blood vessels
Name 4 important mediators released by mast cells:
- Histamine
- Tryptase
- Leukotrines
- Platelet-activating factors
Urticharia is caused by mast cell activation within the epidermis. What mediators are involved and what can urticharia develop into with prolonged exposure?
Mediators:
Leukotrines/cytokines, histamine
If prolonged:
Atopic dermatitis
Eczema
How is angioedema caused in a type 1 hypersensitivity reaction?
Life threatening if affects URT
What is the presentation of anaphylaxis?
Hypotension (CVS collapse)
Generalised urticharia
Angioedema
Breathing problems
Anaphylaxis=
- Acute onset, rapid progressing
- Skin features+ one other organ system
- Patient known to have allergy + bronchoconstriction/GI problem
How should anaphylactic shock be managed?
Multiple doses of epinephrine may be required- 20% of patients= biphasic
How does allergen desnsitisation work?
Administration of increasing doses of allergen extracts over years- given to patients by injection/drops/tablets
(90% effective in patients with bee/wasp anaphylaxis)
