What is the best definition for histimine?

Histamine is a biogenic amine that plays a crucial role in the immune response, acting as a neurotransmitter and regulating physiological functions such as gastric acid secretion and allergic reactions. It is produced by mast cells and basophils in response to allergens and inflammatory stimuli. Histamine binds to specific receptors in the body, leading to various effects, including vasodilation and increased permeability of blood vessels. Its release is a key factor in allergic reactions, contributing to symptoms like itching, swelling, and redness.