BIO 343 Lecture Notes - Lecture 14: Septic Shock, Prostaglandin, Autocrine Signalling
Immunology Chapter 14: Hypersensitivity or Allergic Reactions
Hayden Casassa
• Hypersensitivity is immune response to harmless environmental antigens
• Atopic individuals have genetic predisposition to developing allergies
• Allergens
o Environmental antigens that cause allergic reactions
o Most are small soluble proteins or chemicals
o Most are ihaled or igested ad ross uosal surfaes to APC’s
• 4 different types of hypersensitivities
o Type 1 is mediated by IgE and effector cell is mast cell
• Type 1 (immediate hypersensitivity)
• Triggered by the interaction of allergen with specific IgE bound to FceRI on mast cells
• IgE did ot eole to gie us allergies… ai futio is i iuit agaist ultiellular parasites
o Reaction is triggered by allergen
o Essentially we get triggering of mast cell which causes release of inflammatory mediators
o IgE did’t eole to gie us allergies… ai futio is i iuit agaist ultiellular
parasites
• IgE-mediated respopnse against parasitic helminth worms
o Worms stimulate CD4 TH2 response that leads to B cell production of IgE (IL-4/13), increase of
blood Eosinophils (IL-5), and tissue mast cells (IL-3)
o Worms arent killed by cells so need to be removed by force
o Mediators lead to physical actions like vomiting or diarrhia to remove
o Those infected with parasites rarely have allergies
• Elimination of parasites correlates to higher allergies country-wide
o Referred to as Hygeine Hypothesis
o Excessive hygenic environment may predispose ppl to allergies
• Without worms, IgE lost focus of attention
o In developed countries like US, TH2 arm of immunity is aimed at harmless antigens
• Immediate Hypersensitivity (Type 1) is most common health issue affecting children
• IgE and FceRI
o IgE is not retained in the blood but concetrates in tissues where it binds to high-affinity FceRI on
mast cells
o IgE production requires B cell class switching that is primarily influenced by TH2 cell cytokines
IL-4 and IL-13
o IgE binds its FceRI in the absence of antigen which is expressed on mast cells, basophils, and
activated eosinophils
o The affinity of the interaction of IgE with its receptor is far greater than any other Fc Receptor
find more resources at oneclass.com
find more resources at oneclass.com
o The FceRI consists of the IgE binding alpha chain, Beta chain, and homodimer y chain for signal
transduction
• IgE and FceRI supply each mast cell with a diversity of antigen-specific receptors
o Mast cells acquire IgE made by a variety of B cells
▪ Therefore as shown by picture above they are much more diverse
o One mast cell can have 500,000 FceRI molecules which is more than B cells
▪ Ca hae speifiit for lots of differet thigs hile BCR’s ol recognize one thing
• Cross-linking of FceRI on mast cell by allergen and IgE causes mast cell activation and degranulation
o Without antigen, mast cell contains preformed granules
o When antigen is encountered 2nd time, mast cell degranulates
▪ First exposure triggers specific IgE production
o You need to cross-link them (shown above) in order for signal to be sent
o Within 30 seconds of activation, they release granules
• Xolair, prescription drug consisting of humanized IgG mAb that binds to IgE
o If IgE is what causes allerg… the preet IgE fro idig to ast ell
▪ This prevents mast cell activation
• Mast cells reside in mucosal + epithelial tissues
o Cytoplasm contains granules
o Express many receptors and secrete numerous types of cytokines
o Have beneficial roles in innate and adaptive immunity
▪ Release cytokines that recruit leukocytes to sites of inflammed tissues
▪ Release growth factors that promote repair of damaged tissues
o IL-3 is growth factor for mast cells
• Tissue mast cells orchestrate IgE-mediated reactions through the release of inflammatory mediators
o Overall goal is to attract leukocytes to amplify the reaction started by mast cells
o Two classes of mast cell mediators
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
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