Allergic diseases and pseudo-allergic reactions: definitions, mechanisms, epidemiology

Published on 8 December 2023




EMC – Traité de Médecine Akos 2023 ;0(0) :1-5 [Article 2-0010]


Excessive or aberrant immune responses to tissue-damaging antigens are called immunological hypersensitivity reactions (IHRs). These reactions are classified according to the main mechanism responsible for tissue damage and disease. HSR for which an immunological mechanism has been identified are called allergic HSR, whether immunoglobin E (IgE) or non-IgE dependent. Others are non-allergic HSR and, when symptoms are immediate, involve the non-immunological release of histamine, bradykinin or leukotrienes. For allergic HSR, the Gell and Coombs classification is still valid, with four types identified: type I induced by allergen-specific IgE antibodies; type II cytotoxic, triggered by IgG and IgM antibodies; type III induced by immune complexes (IC); and type IV linked to T lymphocytes. However, with advances in immunology research, new subtypes are being proposed, particularly for type II and IV reactions. The aim of this presentation is to review the nomenclature used in this field, describe the immunological and non-immunological mechanisms behind HSR, and present recent epidemiological data.

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