Inflammatory mediators, including cytokines, histamine, bradykinin, prostaglandins, and leukotrienes, impact the immune system, usually as proinflammatory factors. Other mediators act as regulatory components to establish homeostasis after injury or prevent the inflammatory process. Histamine, a biogenic vasoactive amine, causes symptoms such as allergies and has a pleiotropic effect that is dependent on its interaction with its four histamine receptors. In this review, we discuss the dualistic effects of histamine: how histamine affects inflammation of the immune system through the activation of intracellular pathways that induce the production of inflammatory mediators and cytokines in different immune cells and how histamine exerts regulatory functions in innate and adaptive immune responses. We also evaluate the interactions between these effects. Mast cells, basophils, and platelets all store histamine in their granules. Stimuli that cause acute inflammation, anaphylatoxins, and histamine-releasing factors all release histamine from these cells. In the immediate transitory phase of an acute inflammatory reaction, histamine causes vasodilation and increases vascular permeability. In acute inflammation, this acts as a chemical mediator.

Index Terms- Vasoactive amine, vasodilation, chemical mediator, mast cells.