Type I Hypersensitivity Flashcards
What is type I hypersensitivity and what is it caused by?
It is an allergic reaction provoked by re-exposure to a specific type of antigen referred to as an allergen.
What class of antibodies cause a type I response?
IgE antibodies
When do non-allergic individuals most commonly produce IgE antibodies?
In response to parasitic infections or very potent venoms.
Individuals with allergies produce antibodies against common, multivalent, environmental antigens. What does multivalent mean?
Multivalent refers to the fact that the antigen has multiple sites at which an antibody can attach or be produced
What test can be used to diagnose allergies?
The skin prick test.
What would a positive reaction to the skin prick test look like?
Inflamed, raised tissue. This is otherwise known as a wheal and flare.
What factors can play a role in the initial sensitization of the immune system to an allegen?
The IgE production is complex with factors in genetics, age, and the environment all involved.
What causes the production of IgE antibodies?
B cells being activated by the type 2 cytokines IL-4 and IL-13.
What causes the production of the two type 2 cytokines (which indirectly cause the production of IgEs)?
The generation of type 2 helper CD4 T cells and follicular B helper CD4 T cells.
Where are IgEs found and how is this different from other antibodies?
It is bound to the surface of innate immune cells, especially mast cells and basophils. Most antibodies are found in the circulation.
Why does even a small amount of antigen cause such a relatively large and fast response in type I hypersensitivity?
The granulocytic cells IgE binds to have a high-affinity IgE receptor, called Fc epsilon receptor I. If one of the IgE antibodies bound to the cell detects an allergen, it results in rapid crosslinking and degranulation of the mast cell or basophil.
What are the end products of
the rapid crosslinking and degranulation?
The release of histamine.
A range of cytokines that can recruit other cells and promote further type 2 T helper cell differentiation.
Highly active, smooth muscle contracting molecules such as leukotrienes and prostaglandins.
These are not all released at the same time.
What phases can we split a type I hypersensitivity reaction into?
The early phase, the later response, and the late response (or third response to make things clearer).
What is the early phase of a T1 hypersensitivity reaction?
The result of bioactive small molecules produced directly by mast cells. Occurs within minutes of allergen exposure.
What is the later phase of a T1 hypersensitivity reaction?
It is often seen within a few hours and is the result of the recruitment of early inflammatory cells such as neutrophils.
