Flashcards in Allergies Deck (95):
What does the term hypersensitivity describe?
The antigen specific responses that are either inappropriate or excessive, and result in harm to host
What mechanisms underlie the hypersensitivity immune responses?
Those employed by the host to fight infections
What are the common features of hypersensitivity responses?
What happens in the sensitisation phase of a hypersensitivity response?
First encounter with antigen
What happens in the effector phase of a hypersensitivity response?
Clinical pathology upon re-exposure to same antigen
What are the types of hypersensitivity reactions?
Type I, or immediate
Type II, or antibody mediated
Type III, or immune complex mediated
Type IV, or cell mediated
How quick is the onset of type I hypersensitivity reactions?
What are type I hypersensitivity reactions also known as?
What are type I hypersensitivity reactions a response to?
Environmental non-infectious agents (allergens)
What molecule do type I hypersensitivity reactions involve?
When is the onset of type II hypersensitivity reactions?
What are type II hypersensitivity reactions a response to?
Non-soluble tissue antigens
What molecule do type II hypersensitivity reactions involve?
When is the onset of type III hypersensitivity reactions?
What are type III hypersensitivity reactions a response to?
When is the onset of type IV hypersensitivity reactions?
What is a type IV hypersensitivity reaction a response to?
Environmental infectious agents and self antigens
What kind of diseases are type IV hypersensitivity reactions?
What is happening to the worldwide prevalence of allergies?
It is increasing
How does the incidence of allergy in the UK compare to other countries?
It is in the top 3 countries with the highest incidence of allergy
What % of children in the UK have an allergy?
How many <45 year olds have 2 or more allergies in the UK?
What proportion of children have a peanut allergy in the UK?
1 in 50
How much do allergies cost per year in primary care in the UK?
What is the development of allergy thought to be affected by?
A mixture of genetics and environmental factors
What phenotype often present as non-allergic?
What phenotype often presents as allergic?
How is geographical location related to allergy?
Those from developing countries tend to have less allergies, and those from westernised countries tend to have more allergies
Why do people from developing countries tend to have less allergies?
Large family sizes
Rural homes, lifestock
Intestinal microflora variable/transient
Low antibiotic use
High helminths burden
Poor sanitation, high orofecal burden
Why do those from westernised countries tend to have more allergies?
Small family size
Affluent, urban homes
Intestinal microflora stable
High antibiotic use
Low or absent helminths burden
Good sanitation, low orofecal burden
What are the common allergies?
House dust mite, cockroaches
Tree and grass pollen
What animals are people commonly allergic too?
Domestic pets such as cats and dogs
What insect venoms are people commonly allergic too?
Those contained in wasp and bee stings
Give an example of medicines people are commonly allergic too
The antibiotic penicillin
Give an example of a chemical people are often allergic too
What foods can people be allergic too?
What should be considered with people with allergies?
People with allergies can often have cross-reactions with other associated allergens
What are hypersensitivity reactions caused by?
Activation of mast cells through IgE dependant mechanisms
What is the result of activation of mast cells in hypersensitivity?
These activated mast cells then release chemical mediators
What is the most important chemical mediator in hypersensitivity reactions?
What are the classes of chemical mediators in hypersensitivity reactions?
Give 4 examples of enzyme chemical mediators in hypersensitivity reactions
What are the biological effects of enzyme chemical mediators in hypersensitivity reactions?
Remodel connective tissue matrix
Give two examples of toxic mediators in hypersensitivity reactions
What are the biological effects of toxic mediators in hypersensitivity reactions
Toxic to parasites
Increase vascular permeability
Cause smooth muscle contraction
Give 6 cytokine chemical mediators in hypersensitivity reactions
What are the biological effects of IL-4 and IL-13 in hypersensitivity reactions?
Stimulate and amplify TH2 cell response
What are the biological effects of IL-3, IL-5, and GM-CSF in hypersensitivity reactions?
Promote eosinophil production and activation
Where does the TNF-alpha in hypersensitivity reactions come from?
Some stored preformed in granules
What are the biological effects of TNF-alpha in hypersensitivity reactions?
Stimulates cytokine production by many cell types
What chemokine chemical mediator is released in hypersensitivity reactions?
What are the biological effects of chemokines in hypersensitivity reactions?
Attracts monocytes, macrophages, and neutrophils
Give 4 lipid mediators in hypersensitivity reactions
Leukotrienes C4, D4, E4
What are the biological effects of leukotrienes in hypersensitivity reactions?
Cause smooth contraction
Increase vascular permeability
Stimulate mucus secretion
What are the biological effects of platelet-activating factor in hypersensitivity reactions?
Amplifies production of lipid mediators
Activates neutrophils, eosinophils, and platelets
What does an initial exposure to an allergen cause?
Plasma cells to create an antigen-specific IgE
What happens once an antigen-specific IgE has been produced?
It binds to mast cells to sensitise it to the specific antigen (allergen)
What does second exposure to an allergen cause?
Cross-linking of the IgE molecules on the surface of the mast cell
What does cross linking of IgE molecules on the mast cell trigger?
The release of granule contents, including histamine and chemokines, and synthesis of new mediators; leukotrienes and prostaglandins
What does the release of granule contents from mast cells result in?
A number of physiological changes, such as;
Increased vascular permeability
How is an allergic reaction diagnosed?
Blood/serum levels of mast cell products
Where can the effects of an allergic reaction manifest?
How can the effects of allergic reaction manifest in the epidermis?
Increased vascular permeability and vasodilation results in urticaria (hives)
How does urticaria present?
Creates a wheal and flare type marking on the skin
How can the effects of an allergic reaction manifest in the deep dermis?
Increased vascular permeability and vasodilation results in angiodema of the lips, eye, tongue, and upper respiratory tract
What is the problem with the manifestation of allergic reaction in the deep dermis?
It can carry the risk of suffocation if in the respiratory tract
What can systemic activation of mst cells result in?
How serious is anaphylaxis?
Medical emergency- death if not treated
What happens in anaphylaxis?
Increased vascular permeability leads to hypotension and cardiovascular collapse
Generalised urticaria and angiodema
Bronchoconstriction leads to breathing problems
How many deaths did anaphylaxis result in between 1992 and 2001?
Over 200 but im pretty sure this isnt going to be in the exam so its a pointless fact
When should anaphylaxis be treated?
How should anaphylaxis be treated?
What is the effect of intramuscular adrenaline in anaphylaxis?
Reverses peripheral vasodilation and reduces oedema
Reverses airway obstruction/bronchospasm
Increases force of myocardial contraction
Inhibits mast cell activation
Why is adrenaline said to be a time-saver rather than a life-saver in anaphylaxis?
Reactivation can re-occur in 20% of patients without re-exposure to the antigen
What may be required with adrenaline in anaphylaxis?
What is required with adrenaline in anaphylaxis?
Proper use of the epipen
What is it important to do after treatment with adrenaline in anaphylaxis?
Continue to monitor pulse, BP, ECG, and O2 sats
What factors are considered in a diagnosis of allergy?
Skin prick tests
What clinical history is considered in allergy?
Route of exposure
What blood tests are done in diagnosis of allergy?
Serum allergen-specific IgE
Serum mast cell tryptase, histamine (systemic granulation)
What allergens are skin prick tests done for?
Range of allergens
What is being looked for in skin prick tests?
Wheat and flare reaction of >3mm
What do skin prick tests need?
When is a challenge test done?
Food and drug allergy
What is the problem with challenge tests?
Slight risk of anaphylaxis on highly sensitised patients
How is an allergy managed?
Medic alert information
How can allergens be avoided/eliminated?
Read food levels
House dust mite avoidance
Avoid high risk situations
What education is given in management of allergy?
Parents to recognise symptoms
Patients to use epipen
Call emegency devices when epipen is used
Schools and social activities
What drugs can be given in the management of allergy?
What should be given in antihistamine prevention?
Alternating sedating/non-sedating forms
How can corticosteroids be administered in allergy management?
Give an example of an anti-IgE IgG drug
What does allergen desensitisation involve?
Administration of increasing doses of allergen extracts over a period of years
When is allergen desensitisation used?
In patients with high risk of systemic attack