Leukotrienes are biologically active lipid mediators derived from arachidonic acid through the 5-lipoxygenase pathway, primarily produced by leukocytes such as mast cells, eosinophils, basophils, and macrophages. They play a central role in inflammation, allergic reactions, and immune responses by promoting bronchoconstriction, increasing vascular permeability, stimulating mucus secretion, and attracting inflammatory cells to sites of tissue injury. Leukotrienes are particularly important in the pathophysiology of asthma, allergic rhinitis, and other inflammatory disorders, making them important therapeutic targets for leukotriene receptor antagonists and 5-lipoxygenase inhibitors.