17.5
Reazioni allergiche: Anafilassi
L'anafilassi è una grave reazione di ipersensibilità potenzialmente letale, mediata da anticorpi IgE. Quando le IgE si legano agli allergeni, innescan…
L'anafilassi è una reazione di ipersensibilità immediata mediata da anticorpi IgE. Questi anticorpi si legano agli allergeni, formando complessi di anticorpi allergeni–IgE. Gli allergeni comuni includono polline, acari della polvere, farmaci e alcuni alimenti.
Questi complessi si legano ai recettori dei mastociti e dei basofilo, portando a una rapida degranulazione e al rilascio di istamina, leucotrieni e prostaglandine.
Questi mediatori causano vasodilatazione, broncocostrizione, edema e attivazione dei neutrofili, generando una risposta infiammatoria.
Queste reazioni possono influire gravemente sulla vascolarità, sul tratto gastrointestinale, sulla pelle e sul sistema respiratorio. Possono anche manifestarsi come condizioni come allergie alimentari, orticaria, rinite e asma.
Vari farmaci possono causare anafilassi, tra cui penicillina, asparaginasi, anticorpi monoclonali, corticotropina, eparina, vaccini, anestetici locali e antisettici come la clorexidina.
I metodi diagnostici per l'anafilassi sono clinici, basati sui sintomi. I test cutaneo, come l'iniezione intradrimica di penicilloilpolilisina, possono successivamente identificare l'allergia alla penicillina.
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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.