Types of hypersensitivity in allergic reactions: immune mechanisms and clinical implications

Abstract

Background. Allergic reactions are clinical manifestations of hypersensitivity that occur due to an abnormal immune response to harmless environmental substances such as pollen, food, or dust. These reactions are common, varying from mild symptoms to severe and lifethreatening conditions requiring urgent medical care. Objective(s). Classification of allergic reactions by immunologic hypersensitivity types allows understanding of specific mechanisms and choosing appropriate treatment for each clinical case. Materials and methods. For classifying allergic reactions and analyzing the clinical implications of each immunologic hypersensitivity type, nationally and internationally recognized guidelines were used, including recommendations from the European Academy of Allergy and Clinical Immunology and the American Academy of Allergy, Asthma, and Immunology. Results. Four main types of immunologic hypersensitivity have been identified: Type I, which is immediate and IgE-mediated, responsible for conditions like anaphylaxis, asthma, and urticaria; Type II, cytotoxic and mediated by IgG and IgM antibodies, involved in hemolytic transfusion reactions; Type III, caused by immune complex deposition, commonly seen in systemic lupus erythematosus and serum sickness; and Type IV, delayed and cellmediated, associated with contact dermatitis and the tuberculin skin test. Each type involves distinct immunopathological mechanisms crucial for differential diagnosis and personalized patient treatment. Conclusion(s). Understanding the types of hypersensitivity enables the comprehension of complex allergic reactions and contributes to the establishment of an effective therapeutic plan. Their classification provides an essential framework in internal medicine, clinical immunology, and allergological practice.