Hypersensitivity Flashcards
How do type 2 hypersensitivity reactions result?
They result usually from IgG binding from components of cell membranes or extracellular matrix.
Name an example of type 2 hypersensitivity reaction?
Goodpasture’s syndrome. Antibodies bind to basement membrane collagen type IV. glomerulonephritis in kidney and pulmonary haemorrhage in lung
Describe how haemolytic anaemia is caused by penicillin
Penicillin modifies proteins on human red blood cells. The penicillin red blood cells are phagocytosed by macrophages which then present the penicillin RBC to CD4 T cells. Activation of complement leads to formation of MAC causing lysis of RBC
Describe features of type 3 hypersensitivity
Caused by IgG but sometimes IgM. The antibodies directed to soluble agents. They form antibody-antigen complexes which can be normal but excess can lead to immune complex deposition in tissue leads to pathology
What occurs with excess formation of immune complesed?
It can activate complement which releases inflammatory mediators which can induce mast cell degranulation. This leads to local inflammation.
What are some common sites of immune complex deposition
- Glomeruli,
- Blood vessel walls- Causing vasculitis (often seen as skin lesions close to the skin),
- Synovial membrane- rheumatoid arthritis.
- Skin- Causes rashes,
- Systemic sites- Systemic lupus erythematosus, IC deposits will be in kidneys, joints, skin, vasculature and other organs.
Describe features of type 4 hypersensitivity
It is entirely cell-mediated and complement does not play a role. Most type 4 reactions are caused by CD4+ delayed type hypersensitivity (DTH) reactions - 2 to 4 days after exposure to antigen.
What can occur as a result of DTH responses?
Walling off infectious sites = granulomas.
What is a special category of DTH reactions?
Contact sensitivites when an antigen is not infectious agent but a chemical that binds to cell surface, can be heavy metal sensitivites or poison ivy ect
Describe an example of how a type 2 hypersensitivity is related to an autoimmune disease
Autoimmune haemolytic anaemia (syndrome) and an autoantigen against blood group antigens. Both result in destruction of RBCs and therefore anaemia.
Describe an example of how a type 3 hypersensitivity is related to an autoimmune disease
Rheumatoid arthritis (syndrome) and rheumatoid factor IgG complexes (autoantigen) both result in arthritis.
Describe an example of how a type 4 hypersensitivity is related to an autoimmune disease
Insulin dependant diabetes mellitus (syndrome), and pancreatic beta cell antigen (autoantigen) both result in Beta cell destruction
