Review Note
Last Update: 12/13/2023 09:07 PM
Current Deck: 1 CRNA::Apex Ankisthesia::Ankisthesia::M&M::54 Anesthetic Complications
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Type {{c1::4}} hypersensitivity reactions are mediated by {{c2::CD4+ T}} lymphocytes that have been sensitized to a specific antigen by {{c3::prior exposure}}.
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Ex of type 4 hypersensitivity reactions include: TB skin test, allergic contact dermatitis, Type 1 DM, Hashimoto's thyroiditis, graft v host disease, and multiple sclerosis to name a few.
Type 4 reactions are often called delayed type hypersensitivity as the reaction takes several days to develop. Unlike the other types, it is not antibody-mediated but rather is a type of cell mediated response.
There are two mechanisms for type 4 reaction, each involving T cells:
1. Direct cell cytotoxicity: CD8 cytotoxic T cells kill targeted cells.
2. Inflammatory reaction: effector CD4 T cells recognize antigen and release inflammation-inducing cytokines.
This reaction is caused when CD4 Th1 helper T cells recognize foreign antigen in a complex with the MHC class II on the surface of antigen-presenting cells (APCs). These can be macrophages that secrete IL-12, which stimulates the prolieration of more CD4 Th1 cells. CD4 T cells secrete IL-2 and interferon gamma (inflammation inducing cytokines). Activated CD8 T cells destroy target cells on contact, whereas activated macrophages produce hydrolytic enzymes and, on presentation with certain intracellular pathogens, transform into multinucleated giant cells.
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