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IgG production by plasma cells
1%
3/437
IgM mediated complement activation
2%
10/437
Cross-linking of IgE on mast cells
91%
397/437
Antibody-antigen immune complexes
3%
14/437
Cross-linking of IgG on mast cells
7/437
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This patient has an anaphylaxis reaction to something she ate. Anaphylaxis is mediated by antigen cross-linking of IgE on mast cells leading to activation and the release of several molecules, including tryptase. Anaphylaxis is a type I hypersensitivity reaction that is mediated by the interaction between IgE and mast cells. Mast cells have multiple different IgE antibodies on their surface, and when two or more of the surface antibodies bind to an antigen, the mast cells are activated. Mast cell activation leads to the release of preformed granules containing various substances (including tryptase). Although the diagnosis of anaphylaxis is based on clinical symptoms, elevated serum tryptase levels from labs performed soon after the inciting event may confirm the diagnosis. Arnold and Williams discuss the recognition and management of anaphylaxis. The most common symptoms are dermatologic and respiratory manifestations (occurring in 90% and 70% of cases respectively). The most common triggers are food, insect stings and medications. Typically symptoms are enough to diagnose the condition, however serum levels of histamine and tryptase can aid diagnosis (although they have to been drawn within strict time conditions, which are often difficult to meet). Intramuscular epinephrine is the appropriate initial therapy. Wong et al. conducted a clinical trial with 53 patients to look at the efficacy of a prophylactic regimen for patients with idiopathic anaphylaxis. Patient were classified based upon their typical anaphylaxis symptoms (generalized vs. angioedema) and the frequency of symptoms (frequent vs. infrequent). In patients classified as “generalized-frequent” and “angioedema-frequent”, they found a significant improvement in number of episodes and emergency room visits when treated with prophylactic prednisone, H1 blockade, and sympathomimetic amine therapy. There was no significant effect of prophylaxis In patients classified as generalized-infrequent and angioedema-infrequent. Illustration A depicts the stages of mast cell activation. Illustration B is a diagram of the signs and symptoms of anaphylaxis. Incorrect Answers Answer 1: IgG production by plasma cells plays a role in innate immunity, but is not an underlying mechanism of tryptase production in anaphylaxis. Answer 2: IgM mediated complement activation is the mechanism underlying type II hypersensitivity reactions. Answer 4: Antibody-antigen immune complexes are found in type III hypersensitivity reactions (e.g. systemic lupus erythematosus). Answer 5: Mast cells have IgE, not IgG on their surface, which is responsible for initiating the type I hypersensitivity pathway.
4.8
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