Fig. 5.

Experimental model of transcellular leukotriene biosynthesis. 5LO^−/− mice were lethally irradiated, then rescued with bone marrow cells from LTA₄H^−/− or LTC₄S^−/− mice. Upon zymosan stimulation, cells of a bone marrow origin could synthesize either cysLTs (if donors were LTA₄H^−/−) or LTB₄ (if donors were LTC₄S^−/−), but no single cell could synthesize both. Parenchymal cells could not synthesize either, as they did not express 5LO. To produce both types of LTs, LTA₄ needed to be exported from bone marrow-derived cells and imported into parenchymal cells, then converted to LTB₄ and cysLTs. LTA₄H and LTC₄S were both expressed in the parenchymal cell population, although not necessarily within the same cell.