chap 19 - 1. Hypersensitivity- Response to antigens...

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1. Hypersensitivity- Response to antigens (allergens) leading to damage. *Require sensitizing dose(s). 2. Mechanism of Anaphylaxis (class I): Means “the opposite of protected” from prefix ana(means against) and the Greek phylaxis (meaning protection). Anaphylaxis is an inclusive term for the reactions caused when certain antigens combine w/ IgE antibodies Time before Clinical signs( after a person sensitized to an antigen is re- exposed to that antigen) *<30 min Characteristics: *IgE binds to mast cells or basophils; causes degranulation of mast cell or basophil and release of reactive substances such as histamine. Examples: *anaphylactic shock for drug injections and insect venom; common allergic conditions, such as hay fever, asthma. 3. Systemic Vs. localized anaphylaxis: Systemic anaphylaxis shock from ingested or injected antigens; can result when individual sensitized to an antigen is exposed to it again Localized anaphylaxis hives or asthma from contact or inhaled antigens. 4. Allergy skin test: Is useful in determining sensitivity to an antigen. How it works: *drops of fluid containing test substances are placed on the skin. *A light scratch is made with a needle to allow the substances to penetrate the skin. *Reddening and swelling and itching at the site identify the substance as a probable cause of an allergic reaction. * this small affected area is called a Wheal. 5. Desensitization: Once the responsible antigen has been identified, the person can either try to avoid contact with it or undergo Desensitization. How it works; *consists of a series of gradually increasing dosages of the antigen carefully injected beneath the skin. *the objective is to cause the production of IgG antibodies rather than IgE antibodies in the hope that the circulating IgG antibodies will act as blocking antibodies to intercept and neutralize the antigens before they can react with cell- bound IgE. ** this is not a routinely successful procedure, but it is effective in 65 to 75% of individuals whose allergies are induced by inhaled antigens and in a reported 975 for insect venom. 6. Mechanism of Cytotoxic reactions (Class II): Generally involve the activation of complement by the combination of IgG or IgM antibodies with an antigenic cell. This activation stimulates complement to lyse the affected cell, which might be either a foreign cell or a host cell that carries a foreign antigenic determinant(such as a drug) on its surface. Time before clinical signs:
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chap 19 - 1. Hypersensitivity- Response to antigens...

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