Type I Hypersensitivity Flashcards
Type I hypersensitivity is also called
Immediate hypersensitivity
Define immediate hypersensitivity
Is a type of pathologic reaction that is caused by release of mediators from mast cells
What immune cell is involved in type I hypersensitivity
Mast cells
Type I hypersensitivity is often triggered by what immunoglobulin
IgE Immunoglobulin E
List the two ways antibodies cause diseases
- Antibody mediated (type II)
- Immune complex diseases type III( antibodies against soluble antigens)
- T-cell mediated diseases
In many human immunologic diseases, the damage results from the combination of
Antibody mediated and T-cell mediated diseases
Immediate hypersensitivity causes
Rapid vascular leakage
Mucosal secretion
Followed by inflammation
IgE mediated immediate hypersensitivity reaction are also called
Allergy or Atopy
Sequence events I the development of type I hypersensitivity begins with (6 steps)
- Activation of T-helper 2 cells
- Production of IgE antibodies in response to antigen
- Binding of the IgE to Fc receptor cells
- Exposure to antigens
- Cross linking of the bound IgE by the antigen
- Release of mast cell mediators
Functions of mast cells in type I hypersensitivity
- Rapid increase in vascular permeability
- Smooth muscle contraction
What mast cell mediators recruit neutrophils and eosinophils to site of reaction
Cytokines
What inflammatory component is responsible for tissue injury that results from repeated immediate hypersensitivity
Late-phase reaction
List the mediators found in type I hypersensitivity
Vasoactive amines
Lipid mediators
What 2 cytokines are secreted by T-helper 2
Interleukin -4 (IL-4)
Interleukin -3 (IL-3)
What are the functions of IL-4 and IL-3
Stimulate B lymphocytes specific for the foreign antigens to switch to IgE producing plasma cells
IgE antibody produced in response to an allergen binds to high affinity Fc receptor,specific the Fc chain involved and why
€ heavy chain because they are expressed on mast cells
What term describes the coating of mast cells with IgE
Sensitization
Where are mast cells located
- In all connective tissues
- Adjacent to blood vessels
- Under epithelial tissues
Which of the body’s mast cells are activated by cross linking of allergen specific IgE often depends on
Route of entry of the allergen
The high affinity receptor for IgE called
Fc €RI ( IgE Fc receptor)
Fc€RI consits of 3 polypeptide chains namely
- One binds the FC portion to the € heavy chain very strongly with a Kd of approximately 10^-11
- Other 2 chains of the receptor are signaling proteins
Where else is Fc€RI present
Basophils (circulating cells with many features of mast cells)
Mast cell activation results from
Binding of 2 or more IgE antibodies on the cell
Activation of mast cells trigger biochemical signals from transducing chains of Fc€RI. The signals lead to 3 responses in the mast cells;
- Degranulation (rapid release of granule content)
- Synthesis and Secretion of Lipid mediators
- Synthesis and Secretion of Cytokines
