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Réactions allergiques: anaphylaxie
L’anaphylaxie est une réaction d’hypersensibilité grave, potentiellement mortelle, médiée par des anticorps de type immunoglobuline E, ou IgE. Lorsque…
L’anaphylaxie est une réaction d’hypersensibilité immédiate médiée par des anticorps IgE. Ces anticorps se lient aux allergènes, formant des complexes d’anticorps allergène–IgE. Les allergènes courants incluent le pollen, les acariens, les médicaments et certains aliments.
Ces complexes se lient aux récepteurs des mastocytes et des basophiles, entraînant une dégranulation rapide et la libération d’histamine, de leucotrènes et de prostaglandines.
Ces médiateurs provoquent la vasodilatation, la bronchoconstriction, l’œdème et l’activation des neutrophiles, générant une réponse inflammatoire.
Ces réactions peuvent affecter gravement les vasculaires, le tube digestif, la peau et le système respiratoire. Elles peuvent également se manifester par des affections telles que des allergies alimentaires, de l’urticaire, de la rhinite et de l’asthme.
Divers médicaments peuvent provoquer une anaphylaxie, notamment la pénicilline, l’asparaginase, les anticorps monoclonaux, la corticotropine, l’héparine, les vaccins, les anesthésiques locaux et les antiseptiques comme la chlorhexidine.
Les méthodes diagnostiques pour l’anaphylaxie sont cliniques, basées sur les symptômes. Les tests cutanés, tels que l’injection intradermique de pénicilloylpolylysine, peuvent ensuite identifier une allergie à la pénicilline.
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Q1: What is anaphylaxis and how does it develop?
Anaphylaxis is a severe, immediate hypersensitivity reaction mediated by IgE antibodies. When IgE binds to allergens, it forms complexes that attach to mast cells and basophils, triggering rapid degranulation. This releases mediators like histamine, leukotrienes, and prostaglandins, causing vasodilation, bronchoconstriction, edema, and inflammation throughout the body.
Q2: Which drugs commonly trigger anaphylactic reactions?
Penicillin is responsible for approximately 75% of anaphylactic deaths due to widespread use. Other drugs causing anaphylaxis include asparaginase, monoclonal antibodies, corticotropin, heparin, vaccines, local anesthetics, and antiseptics like chlorhexidine. These reactions occur through IgE-mediated mechanisms similar to food and environmental allergens.
Q3: What body systems are affected during anaphylaxis?
Anaphylaxis primarily affects the cardiovascular, respiratory, gastrointestinal, and integumentary systems. Symptoms include urticarial rash, hives, angioedema, bronchoconstriction, wheezing, shortness of breath, and hypotension. Severe cases progress to anaphylactic shock, characterized by sudden blood pressure drops, respiratory distress, and potential cardiovascular collapse.
Q4: How is anaphylaxis diagnosed in clinical practice?
Anaphylaxis diagnosis is primarily clinical, based on symptom presentation. Skin tests, such as intradermal injection of penicilloylpolylysine, can later identify penicillin allergy. Detecting particular IgE in plasma confirms allergic reactions, though these tests are reserved for cases where the allergen cause remains unclear.
Q5: What are common allergens that cause anaphylaxis?
Common allergens include food items like peanuts and shellfish, environmental substances such as grass pollen and dust mites, insect stings, and pharmaceutical agents. Radiological contrast agents, vaccines, and latex also trigger anaphylaxis. These allergens bind to IgE antibodies, initiating the cascade of mast cell and basophil degranulation.
Q6: What mediators are released during anaphylaxis and what effects do they produce?
Mast cells and basophils release histamine, leukotrienes, and prostaglandins upon degranulation. These mediators cause vasodilation, bronchoconstriction, edema, and neutrophil activation, generating an inflammatory response. The resulting cascade produces symptoms ranging from mild urticaria to life-threatening cardiovascular collapse and respiratory distress.
Q7: How does anaphylaxis differ from other hypersensitivity reactions?
Anaphylaxis is an immediate, IgE-mediated hypersensitivity reaction occurring within minutes of allergen exposure. Unlike delayed hypersensitivity reactions, which develop over hours or days, anaphylaxis causes rapid degranulation of mast cells and basophils. This distinguishes it from other hypersensitivity types in onset speed and severity.