Hypersensitivity reactions (asthma and allergy) Flashcards
What is type 1 hypersentitivity reaction?
Allergy
- Immune reactant = IgE
- Antigen = soluble antigen like allergen
- Effector mechanism involves mast cells which activate the process and hole the IgE on the surface
- Response - allergic rhinitis, asthma or anaphylaxis
What is the wheel and flare reaction?
If you induce the response in a sensitized individual (injection of antigen)
If the mast cells has specific IgE for the presence of specific allergen = cross-linking of mast cells and activation causing vasodilation
Wheel - swelling and tissue odema
Flare - increased vasodilation
Eg. For a mosquito bite - you will see lump as wheel on skin
What is type 2 cytotoxic hypersensitivty?
Caused by when you generate an immune response against a typical molecule which can become sensitized
- For example sticking to red blood cells surface proteins
Immune reactant = IgG (anti-drug antibodies)
- Some are directed at cell-surface receptors which disrupt the normal functions like in Grave’s disease or myasthenia gravis
Antigen = red cell or platelet that becomes coated with the drug
Effector mechanism - activates macrophages and complement resulting in the killing of those cells
What is type 3 hypersensitivtity?
Immune reactant = IgG
Binds to soluble antigen
Effector mechanism - and form immune complexes which are cleared by phagocytes
Includes arthus reaction and serum sickness
What is arthus reaction?
Typically occurs after a vaccination
Immune complexes activate complement which activates mast cells
Inflammatory cells invade the site and blood flow increases
Platelets also accumulate leading to occlusion of the small blood vessels, haemorrhage and appearance of purpura
What is serum sickness?
Caused by large intravenous doses of soluble antigens
IgG antibodies produced form small complexes with the antigen in excess
The complexes are then deposited in tissues like blood vessel walls
Tissue damage is caused by complement activation and the subsequent inflammatory responses
Eg. Following antivenom from snakes
What is type 4 hypersensitivty?
Delayed type
What does Th1 do in delayed-type hypersnesitivty?
What are some examples of type 1 allergy?
Drugs
Pollens
Dust-mite
Nuts
Food
Bites
Animal hair
What is IgE?
- First line of defence against parasitic worms (also pollens and dust mite)
- Binds to mast cells high affinity receptor
- IgE allows mast cells to react when in presence of antigen
How is IgE produced?
Il-4 tells the B cell to switch from IgG to IgE
What causes allergic sensitisation?
Exposure to allergen is critical including:
- Nature of the allergen
- Dosage of the allergen
- Timing
- Location of priming
Role of pro-allergic dendritic cells and cytokines which will induce a Th cell to become Th2 cell, so B cells will produce IgE
Genetic predisposition to allergy
What is filaggrin and atopic dermatitis?
Filaggrin links skin integrity and allergy
When it is defective atopic dermatitis is greater
This is due to the access for allergens
What makes dendritic cell pro-allergic?
What is the early and late phase allergic response?
Early - activation of mast cells by IgE - resulting in localised inflammation, short phase
Late - mediated by T cells, a prolonged phase
- Dependent on allergen dose
What is released from the mast cell during the early and late phase?
What are eosinophils?
- located in the tissues
- recurited to the sites of allergic reactions
- Release highly toxic granule proteins and free redicals upon activation to kill microorganisms and cause tissue damage in allergic reactions
- Synthesise and release prostaglandins and cytokines to amplify the inflammatory response
How does allergy develop?
- Individuals must be sensitised to an allergen before they can react
- Sensitisation requires presentation of allergen to T cells by DC to produce IgE
- The reaction to allergen occurs when the individual is re-exposed to allergen and it binds preformed IgE on mast cells
What is allergic asthma?
- Common allergens causing this includes: pollen, plants and some food
- Can be wheezing breathing, narrowing of airways, rapid changes in airway
Acute response
- Occurs within seconds
- Results in airway obstruction and breathing difficulties
- Caused by allergen-induced mast cell degranulation in the submucosa of the airways
Chronic response
- Caused by activation of eosinophils, neutrophils, T cells and other leukocytes
- Mediators released by these cells cause airway remodelling, permanent narrowing of the airways and further tissue damage
Treatment
- Anti-histamine
- Steroids
- Bronchodilators
