Hypersensitivity Flashcards
What is an antigen?
An antigen is a molecule which can be recognised by an antibody or the adaptive immune system
What is meant by hypersensitivity?
Refers to the undesirable reactions produced by the immune system, including autoimmunity and allergies
What is the name of Type 1 hypersensitivity?
Immediate hypersensitivity / anaphylactic hypersensitivity
What is type 1 hypersensitivity triggered by?
The re-exposure to a specific antigen which is referred to as an allergen
What type of antibodies are type 1 hypersensitivity reactions mediated by?
IgE antibodies
Which cytokines promote the B cell to class switch into an IgE producing cell?
IL-4 and IL-13
Which cells does IgE bind to?
Mast cells and basophils
What receptor do IgE use to bind to the mast cells?
Fc epsilon receptor 1
what happens if an allergen encounters cell bound IgE?
Rapid cross linking and degranulation of the mast cell
What is released when the mast cell degranulates?
Histamine
What affect does histamine have?
Promotes further Th2 differentiation and highly active smooth muscle contracting molecules like leukotrienes
What is the name of Type 2 hypersensitivity?
antibody mediated cytotoxic hypersensitivity
What does type 2 hypersensitivity involve?
The destruction of cells by IgG or IgM antibodies that are bound to antigens present on the surface of cells - normally healthy cells
What are examples of type 2 hypersensitivity reactions?
- Graves disease - antibodies bind to thyrotrophin receptor resulting in the over production of thyroid hormones
- Haemolytic disease of newborns - maternal antibodies can cross the placenta and destroy fetal red blood cells
- Immune thrombocytopenia - antibodies develop gainst platelets
What are the three mechanisms by which Type 2 hypersensitivity reactions can occur?
- Anti-receptor activity
- Antibody dependant cell mediated cytotoxicity
- Classical activation of the complement cascade - formation of membrane attack complexes which results in a destruction of the cells osmotic integrity and
What happens in type 3 hypersensitivity?
When immune complexes are not cleared - leads to an inflammatory response and the attraction of leukocytes
What is an immune complex?
A soluble antigen bound to antibody
What is the difference between complement activation in type 2 and type 3 hypersensitivty?
Type 2 results in small amounts of proteins generated, large amounts in type 3
What affect do C3 and C4 have in type 3 hypersensitivity?
They act as chemokines by attracting neutrophils to the side
What do neutrophils do when they arrive at the immune complex in type 3 hypersensitivity?
They degranulate and result in tissue necrosis and vasculitis
Describe serum sickness?
When a patient is biten by a snake, the venom of the snake enters into the blood stream
Patient is given anti-venom, which the patient produces antibodies against
Therefore during the second bite, immune complexes may be formed
Why is the degranulation of neutrophils so toxic to cells?
They degranulate and release oxygen radicals
What is a membrane attack complex?
When fragments of the complement system come together, they form a MAC which attaches to the cell surface membrane and this creates a channel that allows fluid to pass in and out the cell
What is a membrane attack complex?
When fragments of the complement system come together, they form a MAC which attaches to the cell surface membrane and this creates a channel that allows fluid to pass in and out the cell which disturbs the osmotic integrity of the cell = lysis
