Allergic inflammation

Allergic inflammation is an important pathophysiological feature of several disabilities or medical conditions including allergic asthma, atopic dermatitis, allergic rhinitis and several ocular allergic diseases. Allergic reactions may generally be divided into two components; the early phase reaction, and the late phase reaction. While the contribution to the development of symptoms from each of the phases varies greatly between diseases, both are usually present and provide us a framework for understanding allergic disease cite journal |author=Fireman P |title=Understanding asthma pathophysiology |journal=Allergy Asthma Proc |volume=24 |issue=2 |pages=79–83 |year=2003 |pmid=12776439 |doi= |url=] cite journal |author=Leung DY |title=Molecular basis of allergic diseases |journal=Mol. Genet. Metab. |volume=63 |issue=3 |pages=157–67 |year=1998 |pmid=9608537 |doi=10.1006/mgme.1998.2682 |url=] cite journal |author=Hansen I, Klimek L, Mösges R, Hörmann K |title=Mediators of inflammation in the early and the late phase of allergic rhinitis |journal=Curr Opin Allergy Clin Immunol |volume=4 |issue=3 |pages=159–63 |year=2004 |pmid=15126935 |doi= |url=] cite journal |author=Katelaris CH |title=Ocular allergy: implications for the clinical immunologist |journal=Ann. Allergy Asthma Immunol. |volume=90 |issue=6 Suppl 3 |pages=23–7 |year=2003 |pmid=12839109 |doi= |url=] .

The early phase of the allergic reaction typically occurs within minutes, or even seconds, following allergen exposure and is also commonly referred to as the immediate allergic reaction or as a Type I allergic reaction cite book |author=Janeway, Charles |title=Immunobiology: the immune system in health and disease |publisher=Garland |location=New York |year=2001 |pages= |edition= 5th ed. | isbn=0-8153-3642-X |oclc= |doi= |accessdate=] . The reaction is caused by the release of histamine and mast cell granule proteins by a process called degranulation, as well as the production of leukotrienes, prostaglandins and cytokines, by mast cells following the cross-linking of allergen specific IgE molecules bound to mast cell FcεRI receptors . These mediators affect nerve cells causing itching cite journal |author=Trocme SD, Sra KK |title=Spectrum of ocular allergy |journal=Curr Opin Allergy Clin Immunol |volume=2 |issue=5 |pages=423–7 |year=2002 |pmid=12582327 |doi= |url=] , smooth muscle cells causing contraction (leading to the airway narrowing seen in allergic asthma) , goblet cells causing mucus production , and endothelial cells causing vasodilatation and edema .

The late phase reaction is also sometimes called the Type IV allergic reaction or delayed type hypersensitivity and may take as long as 6 – 12 hours to fully develop following an encounter with allergen . The products of the early phase reaction include chemokines and molecules that act on endothelial cells and cause them to express Intercellular adhesion molecule (such as vascular cell adhesion molecule and selectins), which together result in the recruitment and activation of leukocytes from the blood into the site of the allergic reaction . Typically, the infiltrating cells observed in allergic reactions contain a high proportion of lymphocytes, and especially, of eosinophils. The recruited eosinophils will degranulate releasing a number of cytotoxic molecules (including Major Basic Protein and eosinophil peroxidase) as well as produce a number of cytokines such as IL-5 cite journal |author=Rothenberg ME |title=Eosinophilia |journal=N. Engl. J. Med. |volume=338 |issue=22 |pages=1592–600 |year=1998 |pmid=9603798 |doi= |url=] . The recruited T-cells are typically of the Th2 variety and the cytokines they produce lead to further recruitment of mast cells and eosinophils, and in plasma cell isotype switching to IgE which will bind to the mast cell FcεRI receptors and prime the individual for further allergic responses.

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