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post in: Lifestyle Date:17 Oct 2017, 07:44 views:4175
IgE-mediated anaphylaxis is the classic form of anaphylaxis, whereby a sensitizing antigen elicits an IgE antibody response in a susceptible individual. The antigen-specific IgE antibodies then bind to mast cells and basophils. Subsequent exposure to the sensitizing antigen causes cross-linking explained of cell-bound IgE, resulting in mast cell (and/or basophil) degranulation.
Other types of immunologic anaphylaxis do not involve IgE.
For example, anaphylaxis resulting from administration of blood products, including intravenous immunoglobulin, or animal antiserum is due, at least in part, to complement activation. Immune complexes formed in vivo or in vitro can activate the complement cascade. Certain byproducts of the cascadeplasma-activated complement 3 (C3a plasma-activated complement 4 (C4a and plasma-activated complement 5 (C5a)are called anaphylatoxins and can cause mast cell/basophil degranulation.
When mast cells and basophils degranulate, whether by IgE- or nonIgE-mediated mechanisms, preformed histamine and newly generated leukotrienes, prostaglandins, and platelet-activating factor (PAF) are released. In the classic form, mediator release occurs when the antigen (allergen) binds to antigen-specific IgE attached to previously sensitized basophils and mast cells. The mediators are released almost immediately when the antigen binds.
Certain agents are thought to cause direct nonimmunologic release of mediators from mast cells, a process not mediated by IgE. These include opioids, dextrans, protamine, and vancomycin.
Mechanisms underlying these reactions are poorly understood but may involve specific receptors (eg, opioids) or nonreceptor-mediated mast cell activation (eg, hyperosmolarity).
Inciting agents, the most common inciting agents in anaphylaxis are foods, Hymenoptera stings, and intravenous (IV) contrast materials. Anaphylaxis may also be idiopathic. Immunologic IgE-mediated reactions, typical examples of IgE-mediated anaphylaxis include the reactions to many foods, drugs, and insect stings.