T1 L9: Classification of immunological diseases Flashcards
What are the 5 classifications of immunologically-mediated disease by Gell and Coombes?
Type 1: IgE antibody directed against allergen triggers mast cell degranulation Eg. seasonal rhinitis
Type 2: A pathogenic antibody directly causes disease Eg. autoimmune haemolysis
Type 3: Antobody-antigen complex-mediated disease Eg. lupus
Type 4: Inflammation mediated by T-cells Eg. contact dermatitis tuberculin reaction
Type 5: Hypersensitivity Eg. graves disease
What is haemolytic disease of the new born?
When the D antigen (Rhesus) is not compatible with the mothers causing haemolysis
It causes growth retardation, cardiovascular failure, neurotoxicity from high bilirubin levels
What is done to prevent the consequences of haemolytic disease of the new born during pregnancy?
Rhesus-negative mothers with rhesus-positive partners are given anti-D IgG during pregnancy which prevent sensitisation
It reduces the risk of sensitisation from 16% to 0.1%
What is local immune complex disease?
Painful lesions in the fingertip pulp due to deposition of circulating immune complexes
What are Osler’s nodes?
Cutaneous manifestations of endocarditis
Can also be seen is Lupus
What is endocarditis?
A life-threatening inflammation of the inner lining of your heart’s chambers and valves (endocardium)
What is serum sickness?
A type of allergy where the body reacts to immunogenic drugs or anti-sera produced by animals
Eg. after snake bite envenomation, someone can develop a rash, fever, arthritis, glomerulonephritis
What is extrinsic allergic alveolitis (EAA)?
Also known as hypersensitivity pneumonitis
A patient becomes sensitised to an environmental antigen by repeated exposure so starts producing large amount of IgG antibodies. It causes scarring over time.
Eg. mould spores in hay (farmers lung), pigeon feathers and stool (pigeon-fanciers lung)
What is delayed-type hypersensitivity?
Reactions are mediated by antigen-specific effector T-cells. Takes at least 24 hours to develop
In the skin, its known as contact dermatitis
Eg. poison ivy rash, tuberculin skin test reactions
What are Hapten?
A small molecule which cannot produce an immune response itself but it can bind to a protein to alter its immunogenicity
What is the mechanism behind contact dermatitis?
Sensitising agents are typically highly reactive small molecules which can penetrate the skin.
They react with self-proteins to create protein-Hapten complexes that are picked up by Langerhans cells which present the antigen but sometimes it’s recognised as foreign so T-cells migrate to the dermis
Eg. nickel, molecules in perfumes
What are some positives of the Gell and Coombes classification?
- The only successful attempt to classify disease by mechanism
- A useful framework to describe and understand diseases
What are some negatives of the Gell and Coombes classification?
- Not useful in clinical practice
- Oversimplifies the immunology
- Many diseases are much more complex, particularly chronic inflammatory diseases Eg. rheumatoid arthritis
