Which immune cell type is the main effector in immediate hypersensitivity reactions?

In immediate hypersensitivity reactions, basophils play a crucial role as the main effector cells. When an individual is exposed to an allergen for the first time, the immune system produces immunoglobulin E (IgE) antibodies. These IgE molecules bind to basophils and mast cells, sensitizing them to the allergen.

Upon subsequent exposure to the same allergen, the allergen cross-links the bound IgE on the surface of basophils, leading to their degranulation. This process releases various mediators, including histamines, leukotrienes, and prostaglandins. These substances are responsible for the symptoms associated with immediate hypersensitivity, such as itching, swelling, and bronchoconstriction.

While other immune cell types, like neutrophils and eosinophils, are involved in different aspects of immune responses and inflammation, basophils are specifically central to the mechanism of immediate hypersensitivity due to their involvement in the release of histamines and other inflammatory mediators following allergen exposure. Monocytes also do not play a direct role in immediate hypersensitivity but are more involved in chronic inflammation and delayed-type hypersensitivity.