<prompt> Leukotrienes are produced from ?CholesterolArachidonic acidStearic acidPalmitic acid  <response>: Leukotrienes LTs - They are produced from arachidonic acid. LT B4 is produced in neutrophils; it is the most potent chemotactic agent factor attracting cells to the inflammatory site. The number 4 denotes that there are 4 double bonds in the structure. The 12-lipo-oxygenase in platelets produces 12-HETE hydroxy eicosa tetra-enoic acid and 15-lipo-oxygenase in eosinophils produce 15-HETE. The slow reacting substance of anaphylaxis SRS-A contains LTC4, LTD4 and LTE4 . They cause smooth muscle contraction, constrict the bronchioles, increase capillary permeability, activate leukocytes and produce vasoconstriction. SRS is the mediator of hypersensitivity reactions such as asthma. REF : DM VASUDEVAN TEXTBOOK OF BIOCHEMISTRY, SIXTH EDITION, PG.NO., 165. 