Hypersensitivity Flashcards
Name the four types of hypersensitivity reactions
Type 1: IgE mediated, anaphylactic/immediate
Type 2: antibody-mediated cytotoxicity
Type 3: antibody-antigen immune complexes
Type 4: Delayed or T-cell mediated
What is the function of an IgG antibody?
Highest opsonisation and neutralisation activities
classified into four subclasses
What is the function of IgM antibody
Produced first upon antigen invasion
Increases transiently
What is the function of IgA antibodies?
Expressed in mucosal tissues, forms dimers after secretion
What is the function of IgE antibody?
Involved in allergy
What type of hypersensitivity reaction is an allergy?
What are the two phases?
Type 1 - mediated by IgE antibodies
Immediate hypersensitivity because the reaction happens within minutes
Stage 1: sensitisation
stage 2: re-exposure leading to anaphylaxis
What is a multivalent antigen?
An antigen that has multiple sites of attachment for an antibody to attach to
When do non-allergic individuals produce IgE?
in response to parasitic infections
How can you test for type 1 hypersensitivity?
Skin prick test - expose the skin to small amounts of allergen
check for wheal and flare reactions
What are some common allergens?
Foods, plants, animal dander, drugs (penicillin, sulphonamides) and insect products
What is the sensitisation phase in type 1 hypersensitivity influenced by?
Genetics, environment and age
What does the sensitisation phase result in?
Formation of CD4 t-helper (th2) cells and follicular T helper cells specific to the allergen produce IL-4 and Il-3
This leads to the specific B cells switching from IgM to IgE
Th2 also recruits eosinophils to the site due to IL-5
Once produced IgE is not found in circulation, as it is quickly taken up and bound to the surface of mast cells and basophils
These granulocytes express Fc-epsilon I receptor that binds to the Fc portion of IgE antibodies
When allergen is encountered, cross linking of two IgE bound on the cell membrane of mast cells and basophils leads degranulation of the cell and an immune reaction
Name the 4 main inflammatory mediators.
Histamine
Cytokines
Leukotrines and prostaglandins
Proteases that break down proteins in the extracellular matrix
What does histamine do?
Vascular permeability and smooth muscle constriction, can lead to oedema due to fluid leakage and also urticaria/wheals/red rash
Binds to H1 receptors in airways (bronchi) causing smooth muscle to contract
What do cytokines do?
Recruit and mediate immune response
What do leukotrienes and prostaglandins do?
Vascular permeability and smooth muscle constriction- problem in asthma