Unit 3 - Hypersensitivity Rections Flashcards
What is hypersensitivity damage mediated by?
The same attack mechanisms that mediate normal immune responses to pathogens
- adaptive immune system
What is hypersensitivity?
An exaggerated response of the immune system to ‘foreign’ antigen resulting in tissue damage
What is needed to produce a hypersensitivity reaction?
A sensitisation step is needed as a hypersensitivity reaction cannot manifest upon first exposure
What is another term for hypersensitivity?
Allergy
What is an antigen?
A protein or small molecule which is capable of complexing with protein (hapten)
What is sensitisation?
Antigen contact, typically low-dose via mucous membrane (respiratory, GI tract)
- primary IgE production
What process happens on re-exposure to an antigen?
Pre-formed IgE (allergen-specific) triggers mast cell activitation
Immediate release of mediator (mast cell degranulation) and then early and late phase synthesis of other inflammatory mediators
How long does a hypersensitivity reaction take?
Can occur within seconds - minutes of exposure
Give some examples of hypersensitivity reactions
Allergic asthma Allergic rhinitis (hay fever) Anaphylaxis Food allergy Hives
What are the symptoms of allergic asthma?
Narrowing of airways
What are the symptoms of allergic rhinitis?
Itchy eyes Conjunctivitis Sore throat Ear pain Hearing loss Itchy ears Snoring Mouth breathing Headache Congestion Sneezing Rhinorrhea Congestion Nasal drip
What are the symptoms of a food allergy?
Eczema Itchy mouth Swelling face Swelling tongue Swelling lips Nausea or vomiting Abdominal pain Trouble breathing Dizziness Diarrhoea
What are the symptoms of anaphylaxis?
Normal allergy symptoms as well as:
- swelling of the throat and mouth
- difficulty breathing
- lightheadedness
- confusion
- blue skin or lips
- collapsing and losing consciousness
What is the function of mast cells?
- exert critical proinflammatory functions
- potential immunoregulatory roles in various immune disorders
Mast cell release of mediators such as: histamine, leukotrienes, Cytokines, chemokines, neutral proteases (chymase and tryptase).
Early phase reactants (minutes)
Activates eosinophils
Late phase reactants (hours) Il-4, Il-5, Il-10 Leukotrienes, LTB4, LTC4, cause smooth muscle contraction attract more immune cells like eosinophils, mast cells, neutrophils
Give examples of mediators released by mast cells
- histamine
- leukotrienes
- cytokines
- chemokines
- neutral proteases (chymase and tryptase)
What is the effect of the release of interleukin 5 in a hypersensitivity reaction?
Activates eosinophils
What is the effect of the release of IL-4, IL-5, IL-10, leukotrienes, LTB4 and LTC4?
- smooth muscle contraction
- attract more immune cells e.g. eosinophils, mast cells, neutrophils
Which receptor binds histamine?
H1 receptors
What is the effect of histamine binding to H1 receptor during a hypersensitivity reaction?
Causes smooth muscles around bronchi to contract -> airways get smaller -> DIFFICULTY BREATHING
Causes blood vessel dilation -> increases blood flow -> DECREASES BLOOD PRESSURE
Increased permeability of the blood vessel wall -> leaking into the intercellular space -> OEDEMA (swelling) or URTICARIA (hives)
Give four examples of generic allergic symptoms
- hives (urticaria)
- eczema
- allergic rhinitis
- allergic asthma
How can an allergic reaction be assessed?
- symptoms
- history of allergy
- exposure to allergens
- previous episodes
- family or personal history of asthma, eczema or atopy
- current/previous treatment
- consider other diagnosis including pneumonia
What is Atopy?
A greater tendency in the clinical presentation of Type I hypersensitivity occurring in subjects with a family history of one or other similar conditions
- hay fever
- asthma
- eczema
- urticaria
How might an atopic individual react, despite not suffering from any common allergies?
Immediate wheal-flare skin reactions to intradermal injection of common environmental allergens
What does a raised level of serum IgE indicate?
A diagnosis of an atopic individual, although a normal IgE serum level does not exclude atopy
