Immune Attack: Hypersensitivity Flashcards
How many types of hypersensitivity are there?
4
Which type(s) of hypersensitivity involves IgE?
Type 1
Which antibodies do Type 2 and 3 hypersensitivity involve?
IgM, IgA, IgG
How does type 4 hypersensitivity differ from the other three types?
. Type 4 is ‘delayed hypersensitivity’
. Mediated by T-cells (not antibodies), which release cytokines and over-stimulate macrophages
Which type of hypersensitivity underlies asthma?
Type 1 (involving IgE)
Why do most individuals have very low concentration of IgE in their circulation?
Because IgE antibodies have a very short half-life
Why do mast cells degranulate unnecessarily in atopic individuals? What does this result in?
. Allergen crosslinks mast cells to IgE (atopic individuals have lots of IgE)
. Mast cells degranulate and release excessive histamine and cytokines
. Results in increased vasodilation, vascular permeability, so there’s more cell recruitment and an inflammatory response for an innocuous stimulus
Describe the process by which an allergen binding to a mast cell can result in an allergic response.
. Allergen/pathogen binds to IgE receptor on mast cell (allergen needs to bind to at least 2 IgE antibody receptors for response to be triggered)
. Mast cell degranulates, releasing histamine
. Smooth muscle contraction and increase vessel permeability= oedema/inflammation
Describe how an allergen being engulfed by an APC eventually leads to mast cell degranulation.
. Allergen engulfed by APC–> APC
. APC binds to complementary T-helper 2 cell
. T-helper 2 cells releases IL-4, IL-5, and IL-10 cytokines
. IL-4 causes B-cell to class switch to produce complementary antibodies (i.e. IgE)
. IgE goes into tissues and bind to IgE-Fc receptors on mast cells
. Subsequent entry of allergen causes mast cell to degranulate etc.
Give two key immune features of an atopic individual.
. Have higher than normal levels of IgE in their blood
. More likely to produce T-helper 2 cells than T-helper 1 cells (therefore more production of IL-4, IL-5, and IL-10)
What does IL-10 do?
Activates mast cells to degranulate and release histamine
What does IL-4 do?
Activates B-cells to class switch to produce complementary antibodies
What does IL-5 do?
Activates eosinophils to release cytotoxic granule proteins involve in inflammation
How is the structure of IgE different from other antibodies?
IgE has an extra heavy chain
Summarise the early and late phase responses of atopic individuals.
. Early phase involves mast cells and histamine etc.
. Late phase involves T-cells, eosinophils, and cellular recruitment
