The most impoant cells in type I hypersensitivity ?

Ans. is 'b' i.e., Mast cells Type I hypersensitivity (Immediate hypersensitivity) . 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. . Immediate hypersensitivity reactions are mediated by Ig E, but T and B cells play impoant roles in the development of these antibodies. . Type I reaction requires prior sensitization to a specific antigen (allergen). . Most exposures occur either by inhalation (respiratory route) or ingestion (GIT) of antigen. . Type one hypersensitivity has two phases :? 1) Initial response . After first antigen exposure, this antigen is presented to CD-4 helper T cells (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 paicular 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 ? - Smooth muscle spasm - Increase mucus secretion from the epithelial cells. - Vasodilatation - Increased vascular permeability Recuritment of inflammatory cells Note - Most of the clinical effects are due to smooth muscle spasm.