Hypersensitivity reactions I Flashcards
what is a hypersensitivity reaction
Exaggerated or inappropriate immune response to an antigen/immunogen, causing tissue damage (involves both innate and adaptive immune responses)
2 examples of a Type I (Immediate) hypersensitivity reaction, involving Ig E antibody
Hay fever
Allergic asthma
hives
food allergies
what antibodies do Type II (Cytotoxic) reactions involved e.g transfusion reactions
IgG, IgM antibodies
what is type III hypersensivity reaction, involving IgG, IgM antibodies known as
complex mediated
an example of Type IV (Delayed) reaction, involving T lymphocytes and macrophages
Contact dermatitis (eczema)
When does a type I hypersensitivity reaction occur
immediately after contact with an immunogen/allergen
what antibody is produced in a type I hypersensitivity reaction by plasma cells
IgE
what response do parasites cause
they trigger an TH2 response where B cells produce parasite-specific IgE and so an inflammatory response so parasites get ejected from human host
what does IgE bind to on the surface of mast cells and basophils to release inflammation mediators (asthma, hay fever)
Fc receptors
allergen
an immunogen which causes an allergy eg
* pollen
* animal dander
* house dust mite faeces
* food allergens : nuts; shellfish, eggs
* bee and wasp venom
Allergenicity
the ability of an antigen to induce the abnormal immune response (Th2 mediated)
Atopy
the genetic predisposition to produce IgE
what are normal serum IgE levels
0.1-0.4
how many types of IgE receptors are there which differ in IgE affinity
2
whats the low affinity IgE receptor known as
CD23
what cells is the high affinity IGE receptor (FceRI) expressed on
mast cells and basophils (also some eosinophils, platelets and monocytes)
how many polypeptide chains does High affinity receptor IgE FceRI have
4 polypeptide chains:
▪ alpha, beta and 2 identical gamma chains
OR
alpha, and 2 gamma chains (on monocytes and platelets)
what are Mice lacking FceRI alpha chain resistant to
anaphylaxis (reaction)
what is the Key cell in the orchestration of the inflammatory response
mast cell
where is mast cell found
skin, connective tissues, and mucosal epithelial tissue of respiratory, digestive and genitourinary tract.
what receptors do mast cells express on their surface
high-affinity IgE receptors
what do cytoplasmic granules in mast cells contain which are repsonsible for many signs of allergic reactions
preformed mediators (Histamine, Heparin, Chymase, Tryptase)
Membrane-derived mediators (Leukotrienes; prostaglandins)
what initiates mast cell degranulation
IgE cross linkage, anaphylatoxins (C3a, C5a) and drugs
what protein gets activated when there’s IgE receptor cross-linkage, leading to phosphorylation reactions and generation of second
messengers
Activates protein tyrosine kinase (Lyn)
what mineral is involved when there is IgE cross-linkage and how
calcium
theres an uptake of extracellular calcium and a release of intracellular calcium stores
what acid is formed when phospholipase A2 enzyme is activated in IgE receptor cross linkage
arachidonic acid (inflammation)
type I hypersensitivity reaction sequence of events (6)
- allergen absorbed through the mucosa
- APC presents the processed allergen
- B cells produce specific IgE (t cells help)
- allergen-specific IgE binds to mast cells via Fc receptors
- Re-exposure (allergen cross-links surface-bound IgE)
- Mast cell degranulates
3 consequences of a type I hypersensitivity reaction
anaphylatic shock
food allergies
hay fever
allergic asthma
whats anaphylactic shock usually caused by
systemic release of mast cell mediators
where do airborne allergens triggers mast cell degranulation in hay fever
the nasal mucosa
what happens in allergic asthma un the lower respiratory tract
◼ Bronchial hyperreactivity
◼ Inflammatory infiltrate into the mucosa and submucosa
◼ Epithelial layer denudation/damage
◼ Goblet cell hyperplasia and excessive mucus secretion
◼ oedema (excess water fluid)
◼ bronchoconstriction
