IgE binds to which cell-
Ans. is 'c' i.e.. Mast cells o IgE binds to Mast cells and basophils, and mediate Type I hypersensitivity.Type 1 hypersensitivity ( Immediate hypersensitivity)o It is a rapidly developing immunological reaction occuring within minutes after the combination of an antigen with antibody bound to mast cells in individuals previously sensitized to the antigen,o Immediate hypersensitivity reactions are mediated by Ig E, but T and B cells play important roles in the development of these antibodies.o Type I reaction requires prior sensitization to a specific antigen (allergen),o Most exposures occur either by inhalation (respiratory route) or ingestion (GIT) of antigen,o Type one hypersensitivity has two phases1. Initial response# After first antigen exposure, this antigen is presented to CD-4 helper T ceils (TH2 type) by antigen presenting cells.These primed TH, cells release IL-4 that acts on B-cells to form Ig E specific for that particular antigen.The antigen specific Ig E antibodies then bind to the surface receptors of mast cells and basophils.The process from first antigen exposure to the coating of mast cells by Ig E acts as sensitization (prior sensitization) and first exposure is also called priming or sensitizing exposure (dose).Subsequent exposure {shocking dose) to same antigen then result in activation of mast cells and basophils with release of mediator from these cells that leads to -o Smooth muscle spasmo Increase mucus secretion from the epithelial cells,o Vasodilatationo Increased vascular permeabilityo Recuritment of inflammatory cellsNote - Most of the clinical effects are due to smooth muscle spasm.2) Late phase responseIn this phase additional leukocytes are recruited.These cells amplify and sustain the inflammatory response without additional exposure to the triggered antigen.Among the cells that are recruited in the late-phase reaction, eosinophils are particularly important.Eosinophils produce major basic protein and eosinophilic eataionic protein that are toxic to epithelial cells.Platelet activating factor (PAF) recruits and activates inflammatory cells and is most important cytokine in the inititiation of late phase response.o Type I hypersensitivity occurs in two forms :jAnaphvlaxis - Acute, potentially fatal, systemic. Atopy - Chronic, non-fataL localized.Remembero Mast cells are the most important cells in type I hypersensitivity.o Eosinophils are the most important cells in the late phase reaction of type l hypersensitivity.o Histamine is the most important mediator in type 1 hypersensitivity.o IL-4 is particularly important, it is essential for turning on IgE secreting B cells,o PAF is the most important cytokine in the initiation of late phase reaction,o Most potent eosinophilic activating cytokine is IL-5.
T cells
B cells
Mast cells
NK cells
Immunology