SYNERGISTIC ENHANCEMENT OF MITOGEN RESPONSES OF HUMAN-LYMPHOCYTES BY INHIBITORS OF CYCLOOXYGENASE AND 5,8,11-EICOSATRIYNOIC ACID, AN INHIBITOR OF 12-LIPOXYGENASE AND LEUKOTRIENE BIOSYNTHESIS

Blood mononuclear cells are well-known producers of various cyclo-oxygenase and lipoxygenase metabolites of arachidonic acid, some of which possess immunoregulatory functions. In the present investigation, we have examined 3H-thymidine incorporation in human blood lymphocytes cultured with polyclonal mitogens and antigens in the presence of various inhibitors of cyclo-oxygenase (such as indomethacin and meclofenamic acid) and an inhibitor of 12-lipoxygenase and leukotriene biosynthesis, 5,8,11-eicosatriynoic acid (ETI). It was observed that these inhibitors could augment mitogen responses of nonpurified lymphocyte preparations but not of preparations which were depleted of monocytes. The results indicate that monocytes and not lymphocytes were the main producers of immunosuppressive eicosanoids derived from arachidonic acid. Further, mitogenic responses in the presence of both an inhibitor of cyclo-oxygenase and ETI were augmented to a higher extent than expected. Again, this enhancement was not observed in preparations depleted of monocytes. Arachidonic acid metabolism was examined in mitogen-stimulated cultures pulsed with 14C-arachidonic acid. It was observed that the production of three metabolites was inhibited by meclofenamic acid, whereas the amounts of another 14Cr-labeled compound was almost doubled in the presence of meclofenamic acid.