In the context of drug reactions, type I hypersensitivity reactions are characterized by which mechanism?

Type I hypersensitivity reactions are characterized by an IgE-mediated immune response. This type of reaction occurs when an individual is exposed to an allergen for the first time, leading to the production of immunoglobulin E (IgE) antibodies. These IgE antibodies bind to mast cells and basophils, sensitizing them to the allergen.

Upon subsequent exposure to the same allergen, the allergen cross-links the IgE antibodies on these sensitized cells, triggering them to degranulate. This degranulation releases various mediators, including histamine, leukotrienes, and prostaglandins, which are responsible for the clinical features of immediate hypersensitivity, such as urticaria (hives), allergic rhinitis, asthma, and anaphylaxis.

This mechanism is distinct from other types of hypersensitivity reactions. For instance, delayed cell-mediated responses involve T cells and occur over 24-48 hours, which is characteristic of Type IV hypersensitivity. Cytotoxic antibody-mediated responses involve IgG or IgM antibodies binding to antigens on cell surfaces, leading to cell destruction, typical of Type II hypersensitivity. Immune complex-mediated responses involve the formation of antigen-antibody complexes that deposit in tissues, causing inflammation and damage