Hypersensitivity part 2 Flashcards
What specific allergies should you include in a history?
Patients LIE
- Latex
- Iodine
- Elastoplast
What immune reactant is included in a type 2 hypersensitivity reaction?
IgG
How many different types of hypersensitivity reactions are there?
4
In which immune reaction is there no antibody involved?
Type 4
Driven by T cell activity
Give an example of a type 2 hypersensitivity reaction and how it works
Goodpasture’s syndrome, antibodies bind to basement membrane collagen type 4, glomerulonephritis in kidney, pulmonary haemorrhage in lung.
- 100% have nephritis
- Around 50% have lung problems
Give an example of a drug which can cause a type 2 hypersensitivity reaction
Penicillin
Describe how a type 2 hypersensitivity reaction works
- Binds to proteins that coat the surface of RBC
- Creates neoepitope
- This substance is taken up by macrophages/dendritic cells
- Broken up and presented to T cells
- Activate specific CD4 T cells to become TH2 cells
- B cells are activated by antigen and by help from activated TH2 cells
- Plasma cells secrete penicillin-specific IgG which binds to modified RBC
- Penicillin-specific IgG binds to penicillin-modified proteins on RBC
- Activation of compliment components C1-C9 and formation of membrane-attack complex causes lysis of RBC
- Activation of compliment components C1-C3 leads to covalent bonding of C3b and phagocytosis of antibody - and compliment-coated RBC
What antibodys are involved in type 3 hypersensitivity?
IgG but sometimes IgM
What system usually clears antibody-antigen complexes?
Reticuloendothelial system (RES): Macrophages, neutrophils in liver spleen and bone marrow that ingest and degrade immune complexes
How does a type 3 hypersensitivity reaction work?
- Antibody-antigen complexes form and too many are made and not cleared
- Complement releases inflammatory mediators C5a, C3a and C4a. C5a also induces cell degranu,ation
- Local inflammation, movement of fluid and protein into tissue and blood vessel is occluded
- Over the course of 1-2 hrs
What are the common sites of immune complex deposition? (type 3 reaction)
- Glomeruli
- Blood vessel walls
- Synovial membranes
- Skin
- Systemic sites
In what reaction does compliment not play a role?
Type 4
How long does it take for there to be a reaction to type 4 hypersensitivity?
2 to 4 days
Describe how a type 4 hypersensitivity reaction works?
- Antigen is introduced into subcutaneous tissue and processed by local antigen-presenting cells
- A TH1 effector cell recognises antigen and releases cytokines which act on vascular endothelium
- Recruitment of T cells, phagocytes, fluid, and protein to site of antigen injection causes visible lesion
Give some examples of type 4 / DTH reactions
- Listeria
- Leishmania
- M. tuberculosis
- M. Leprae