Hypersensitivity Flashcards
Describe the structure and function of each antibody (IgM, IgE, IgG, IgA, IgD)
IgM - tetramer - released at beginning of infection
IgG - highly specific targeting specific epitopes
IgE - developed in response to parasitic threats - implicated in allergy, particularly alongside eosinophils
IgA - mucosal tissue - form dimers and important in neonatal gut expressed in breast milk
IgD - monomers, unknown function - possibly implicated in function and induction of antibodies in B cells.
What classification system is used to divide hypersensitivity reactions?
Gell and Coombs classification
What is a type 1 hypersensitivity reaction? Which antibodies are produced? How long does a response take? Give an example of a T1 hypersensitivity reaction
Characterised by the production of IgE antibodies in response to an antigen.
Cross linkage of surface IgE receptors on mast cells or basophils causes degranulation and release of mediators such as histamine.
Response is rapid - minutes.
Typical of people with atopy eg. hay fever or asthma.
Anaphylaxis is an example of a T1 hypersensitivity reaction causing widespread release of histamine.
What is the management for anaphylaxis?
Adrenaline 0.5mg IM (epipen)
Steroids to turn off secondary immune response
Antihistamines
Observation for at least 12h
What is a type 2 hypersensitivity reaction? Which antibodies are responsible? Give an example of a T2 hypersensitivity reaction.
Treatment for T2 hypersensitivity reaction?
Caused by IgG or IgM antibodies binding to a fixed antigen in a tissue. Binding of the antibody may activate complement and lead to cellular injury or change cellular function.
These cause autoimmune diseases, transfusion reactions, antiglomerular basement membrane disease, good pasture syndrome.
Treatment: plasmapheresis, immune suppression (steroids) and supportive treatment (ventilation, harm-dialysis, filtration to help kidneys)
What is a type 3 hypersensitivity reaction? Which antibodies are responsible? Give one example of a type 3 hypersensitivity reaction.
IgM or IgG antibodies circulate and form immune complexes with antigen in the blood and deposit in tissues where they activate complement.
Small blood vessels, kidneys and joints are common places.
Tend to be multi-system diseases such as vasculitis, arthritis, glomerulonephritis, pneumonitis.
What is a type 4 hypersensitivity reaction? Which immune cells are responsible? Give an example
Caused by activated T cells that injure cells directly by killing or release of cytokines which activates macrophages.
T cell responses take 1-2 days so response is delayed.
Examples: contact dermatitis, Hashimoto’s thyroiditis, PBC, TB.
