Leukotriene are synthesized mostly in of myeloid origin cells, like basophils, eosinophils, macrophages, monocytes, stem cells...
The initial step in the synthesis of leukotrienes is the cleavage of an arachidonoyl ester bond of a glycerophospholipid through the action of a PLA2 in a hydrolysis reaction that yields lysophospholipid and free arachidonic acid. Cellular levels of arachidonic acid and lysophospholipid are tightly regulated; one of the main mechanism that the cell use to mantain the right equilibrium is the so called Lands cycle. In this cycle arachidonic acid is conjugated with CoA through an acyl-CoA ligase and then is esterified to a lysophospholipid by a LAT (lysophospholipid-acylCoA acyltransferase). Inhibition of this enzyme with organo-mercury compound, like thimerosal, leads to a dramatic increase of LTB4 released by PMNs cells (link).
Leukotriene biosynthesis begins with the specific oxidation of arachidonic acid by a free radical mechanism as a consequence of interaction with 5-LO. A second enzymatic step is also catalysed by 5-LO and involves removal of a hydrogen atom from C-10, resulting in formation of the conjugated triene epoxide LTA4.