EFFECT OF PGE(2) AND OF AGENTS THAT RAISE CAMP LEVELS ON MACROPHAGE ACTIVATION-INDUCED BY IFN-GAMMA AND TNF-ALPHA

The effect of prostaglandin (PG) E(2) on macrophage activation by inte rferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) w as evaluated, Murine macrophages infected with Leishmania enriettii or Leish mania major were activated by exposure to IFN-gamma (10-50 U/ml ) and TNF-alpha (30-3000 U/ml), leading to intracellular parasite dest ruction within 24-48 h, Leishmanicidal activity was markedly increased when activation was performed in the presence of PGE(2) (10(-9)-10(-7 ) M) or arachidonate (10(-5) M, a PG precursor), concomitant with enha nced nitrite release and glucose oxidation through the hexose monophos phate shunt pathway, Conversely, activation was reduced by indomethaci n and hydrocortisone, two inhibitors of PG synthesis, Parasite killing and nitrite production were fully restored by exogenous PGE(2), indic ating that inhibition by these drugs was related to their ability to b lock PG production, PG can stimulate adenylate cyclase, thus raising i ntracellular cAMP levels, Accordingly, dibutyryl cAMP, theophylline (w hich prevents cAMP breakdown), and forskolin (an activator of adenylat e cyclase) all stimulated macrophage activation, Finally, PGE(2) and c AMP enhanced expression of inducible nitric oxide synthase mRNA in res ponse to IFN-gamma) and TNF-alpha, and this effect was inhibited by th e cAMP antagonist 2'-O-methyl adenosine, These findings are consistent with the hypothesis that PGE(2) acts as a positive agonist in macroph age activation by IFN-gamma and TNF-alpha via its capacity to modulate intracellular cAMP levels.