Allergic rhinitis is which type of hypersensitivity reaction?
Pathogenesis of allergic rhinitis Allergic rhinitis is a type I hypersensitivity. It occurs in two phases:? 1) Initial response/Acute or early phase 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 results in activation of mast cells and basophils with release of inflammatory mediators Histamine (most impoant) PAF Heparin Cytokines (IL-1, 3, 4, 5, 6; INF) Leukotriens (B4, Ch D4) Eosinophil chemolactic factor (ECF) PGD2 Neutrophil chemolactic factor (NCF) The release of these mediators result in : - Increased vascular permeability and vasodilatation which result in tissue edema - Nasal blockage and sneezing. Smooth muscle spasm - Bronchoconstriction Hyperactivity of glands - Rhinorrhea Recruitment of inflammatory cells. 2) Late phase response Recruited inflammatory cells of initial phase amplify and sustain the inflammatory response without additional exposure to the triggered antigen. PAF is the most impoant mediator in initiation of late phase response. Eosinophils are paicularly impoant cells among the recruited cells which also include neutrophils, basophils, monocytes and T-cells. It causes symptoms like nasal congestion and post nasal drip.
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