30th August 2024

Hypersensitivity

Hypersensitivity reactions are inadequate or exaggerated immune mediated responses to an allergen or antigen. These can be divided to five types:

1. Type I reactions occur when an antigen reacts with immunoglobulin E (IgE) bound to mast cells, as seen in anaphylactic reactions. Conditions such as asthma, eczema, and urticaria are also classified as Type I reactions.
2. Type II reactions involve immunoglobulin G (IgG) or immunoglobulin M (IgM) binding to antigens. Diseases such as pernicious anaemia and Goodpasture’s syndrome fall under this category.
3. Type III reactions are immune complex mediated. These reactions can cause systemic lupus erythematosus and allergic alveolitis.
4. Type IV reactions are delayed hypersensitivity reactions mediated by T cells. Examples include Guillain-Barré syndrome, multiple sclerosis, and graft-versus-host disease.
5. Type V has been a recently recognised reaction in which auto antibodies bind to the cell surface receptors in e.g. myasthenia gravis.

Reference

Descotes J, Choquet-Kastylevsky G. Gell and Coombs’s classification: is it still valid? Toxicology. 2001 Feb 2;158(1-2):43-9. doi: 10.1016/s0300-483x(00)00400-5. PMID: 11164991