Allergy I Flashcards
What are the 3 types of allergies that can occur?
- Allergic contact dermatitis & respiratory hypersensitivity (e.g. asthma, rhinitis)
- Xenobiotics (e.g. some drugs)
- Foods
What is a wheal and flare response & what does it cause?
It occurs during an allergic reaction, dependent on IgE and mast cells.
Histamines are released from mast cells causing inflammation, later producing a late-phase reaction causing increased leukocytes, basophils, eosinophils, etc.
What do mast cells NOT do?
They don’t phagocytose.
Which substance produces the immediate reaction, and which the late-phase reaction?
Immediate: histamines, lipid mediators
- They induce vasodilation, vascular leak, broncho-constriction & intestinal hyper-motility
Late-phase: cytokines
- They induce tissue damage & inflammation
Which cells are involved in an allergen response?
- Eosinophils - releasing granular proteins
- Mast cells
- Basophils
- TH2 cells
- IgE antibodies
- IL-4, IL-5, 1L-13
What is the difference between TH1 and TH2 cells?
TH1: stimulate cellular response , e.g. macrophage initiation, and stimulation of B cells to produce IgM.
TH2: involved in the humoral response, promoting B cell proliferation and inducing antibody production.
Which type of T cell is biased towards TH2 cell (humoral) responses?
CD4 T-helper cells
What is the process in which an allergic reaction is produced?
- 1st exposure to allergen
- Activation of TH2 cells, & stimulation of IgE (antibodies) in B cells
- IgE binds to mast cells
- Allergen is exposed to mast cells
- Mast cells are activated and release mediators
- Immediate reaction occurs mins. after repeated exposure to allergen
- Late phase occurs due to cytokine release
Which type of cell can be defective in an allergy?
TH1.
What is the hygiene hypothesis?
It proposes that early childhood infections can stimulate TH1 cells, causing a natural balance between TH1 and TH2 & develop their immunity.
What can a reduction in childhood infections cause?
Lack of TH1 stimulus, so a TH2 bias is produced, this increases the risk of allergies arising.
Which antibody is specific for worms and parasites?
IgE.
How do chronic worm infections lead to no allergies occurring?
- Parasitic infections cause a high non-specific IgE amount
- As IgE binds, it saturates all the receptors on mast cells and degranulation occurs
- High levels of IL-10 occur, which induces T regulatory cells to switch off this immune system response
- Allergies hence do not occur.
People who have an immunity/intolerance to insect venom/foods/cats/rat urinary allergens have which antibody in their system?
They have IgG4, which does not bind to mast cells (unlike IgE)
Which interleukin is responsible for the IgG4 and IgE gene, and what does it do?
IL-4.
It can splice the IgM gene from a B cell into IgG, or IgA antibodies.
