Thursday, June 25, 2009

Hipersensitivitas

1. Faktor Penyebab Reaksi Hipersensitifitas (Anafilaktif)
Anaphylaxis is a severe, whole-body allergic reaction. After an initial exposure ("sensitizing dose") to a substance like bee sting toxin, the person's immune system becomes sensitized to that allergen. On a subsequent exposure ("shocking dose"), an allergic reaction occurs. This reaction is sudden, severe, and involves the whole body.
Some drugs (polymyxin, morphine, x-ray dye, and others) may cause an "anaphylactoid" reaction (anaphylactic-like reaction) on the first exposure.[6] This is usually due to a toxic reaction, rather than the immune system mechanism that occurs with "true" anaphylaxis. The symptoms, risk for complications without treatment, and treatment are the same, however, for both types of reactions. Some vaccinations are also known to cause "anaphylactoid" reactions.[7] Antitoxins and antivenins may cause similar reactions.
Anaphylaxis can occur in response to any allergen. Common causes include insect bites/stings, food allergies (peanuts and tree nuts are the most common, though not the only), and drug allergies. Pollens and other inhaled allergens rarely cause anaphylaxis. In opthamology, the dye fluorescein used in some eye exams is a well known trigger. Some people have an anaphylactic reaction with no identifiable cause (idiopathic).
The most common cause of anaphylaxis is food, which is followed by insect venom. Allergy to latex rubber is becoming a rapidly increasing problem because the use of latex rubber gloves in the medical field and also an increase in atopy. Exercise, vaccines, and semen account for rare causes of anaphylaxis. In addition, allergen immunotherapy(desensitization) may cause anaphylaxis (Ewan, 1998). See the following table outlining common causes of anaphylaxis.
Common causes of anaphylaxis
· Foods
· Bee and wasp stings
· Drugs
· Latex rubber
A. Foods commonly causing anaphylaxis
· Peanuts
· Tree nuts (eg, brazil nut, almond, hazelnut)
· Fish
· Shellfish
· Egg
· Milk
· Sesame
· Pulses (other than peanuts)
B. Drugs causing anaphylaxis or anaphylactoid reactions
· Antibiotics (especially penicillin)
· Intravenous anesthetic drugs
· Aspirin
· Non-steroidal anti-inflammatory drugs
· Intravenous contrast media
· Opioid analgesics

2. Mekanisme Respon Immun Reaksi Anafilaktif
Immunological Mechanism of Anaphylaxis follow a lot of steps :
(1) Antigen-presenting cell internalizes antigen.
(2) The APC processes the internalized antigen.
(3) The APC presents the processed peptide to CD4+ T lymphocytes via MHC II.
(4) After the peptide is presented, the T cell differentiates into TH2 lymphocytes and produces IL-4, IL-5, IL-9, and IL-13.
(5) IL-4 and IL-13 cause B cell immunoglobulin isotype switching to IgE.
(6) The circulating IgE binds to the IgE receptors on mast cells.
(7) Antigen similar to the original antigen cross-links the mast cell surface-bound IgE, resulting in cellular degranulation. Degranulation releases histamine, tryptase, and other mediators that produce the symptoms of anaphylaxis (Anaesthesia UK, 2005).

Anaphylaxis occurs when a person is reexposed to a specific antigen that cross-links antigen- specific IgE molecules, which are bound to mast cells and basophils. This leads to activation and degranulation of mast cells and basophils. Preformed mediators, such as histamine and tryptase, within the mast cell and basophil are released in degranulation. The metabolism of arachidonic acid in the cell membrane produces other mediators, such as prostaglandins and leukotrienes.

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