Hypersensitivity Type I and II Flashcards
What causes type I hypersensitivity reactions?
Allergens
What is an allergen?
An antigen which elicits an immediate allergic reaction
Which type of antibody is assciated with type I hypersensitivity reactions?
IgE
How many receptors bind IgE?
2
Typically what is IgE associated with?
Control of parasitic infection
What receptors bind to IgE?
- FcεRII (low affinity receptor)
- FcεRI (high affinity receptor)
How much IgE is usually bound to FCεR1?
The receptors are usually saturated with IgE despite a low IgE concentration in the serum as they bind with high affinity
How can a type 1 hypersensititivity reaction lead to anaphylaxis?
- Becomes systemic
- Blood pressure falls
- Bronchospasm
How are mast cells activated by IgE?
- Only activated if IgE is crosslnked by a specific allergen
- Triggers degranulation of mast cell and an inflammatory response
Why is IgE mediated mast cell activation beneficial?
- Can rapidly recruit other leukocytes upon infection
- Inflammatin induced causing increased flow of lymph
- Chemical mediators cause smooth muscle contraction which can help expel pathigens from lung and/or gut
What causes class switching of B cells to produce IgE?
Induction by Th2 T cells
How do inhaled corticosteroids help treat asthma?
Block the delayed response in the lung, inhibiting influx of eosinophils, basophils, lymphocytes
What antibodies mediate a type II hypersensitivity reaction?
IgG and IgM
Where do antibodies bind in type II hypersensitivity reactions?
To cells/components of ECM
What is the major difference between type II and III hypersensitivity reactions?
In type II the antibodies bind to antigen on a cell/component of ECM but in type III antibodies bind to a soluable antigen
What does the classical complement cascade lead to activation of?
Membrane attack complex
What are the 3 main mechanisms of tissue damage which occur in a type II Hypersensitivity reaction?
- Phagocytosis
- Antibody dependent cellular cytotoxicity
- Classical complement cascade
How does phagocytosis become frustrated in type II hypersensitivity reactions?
- Binding to FcR and complement R activates phagocytosis
- Leads to lysosomal contents being exocytosed and necrosis at site of reaction
What happens in transfusion reactions?
- Type II hypersensitvity
- Extensive destruction of donor blood cells
- Results in fever, vomiting
What type of antibody causes transfusion reactions?
IgM
What type of antibody causes haemolytic disease of foetus and newborn?
IgG
How is haemlytic disease of foetus and newborn prevented?
- Anti-RhD antibodies are injected in RhD mother at 28 weeks and after birth
- Binds to foetal RBCs, eliminating them and preventing maternal sensitisation
What is autoimmune haemolytic anaemia?
Antibodies against patient’s own erythrocyte antigens can arise spontaneously or be induced by drugs
How can drugs cause autoimmune haemolytic anaemia?
- Drug binds to RBCs
- Antibodies produced against drug
- Drug:antibody complexes bind RBC
