In Type I hypersensitivity, which cells are primarily involved in releasing mediators such as histamine?

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Type I hypersensitivity hinges on immediate release of mediators from mast cells and basophils. These cells carry IgE antibodies bound to high-affinity FcεRI receptors. When an allergen cross-links the IgE on these receptors, it triggers rapid degranulation, dumping histamine and other mediators into the surrounding tissue. Mast cells reside in tissues like skin, airways, and the GI tract, while basophils circulate in the blood and can migrate to sites of inflammation. The histamine release from these two cell types causes the classic immediate symptoms: vasodilation, increased vascular permeability, bronchoconstriction, and smooth muscle effects.

Other cell types mentioned, such as T lymphocytes, macrophages, and dendritic cells, play roles in antigen presentation, cytokine signaling, and later phases of allergic responses, but they are not the primary sources of histamine in the immediate Type I reaction.