REGULATION OF NEUTROPHIL-DERIVED IL-8 - THE ROLE OF PROSTAGLANDIN-E(2), DEXAMETHASONE, AND IL-4

Historically the neutrophil has been perceived as a terminally differe ntiated leukocyte with limited ability to produce de novo proteins. Fu rthermore, in the context of acute inflammation the activated neutroph il has been appreciated only for its ability to release various protea ses, reactive oxygen, and arachidonic acid metabolites. Recently, the neutrophil has been shown to have the capacity to produce a number of cytokines that may be instrumental in orchestrating the progression of acute inflammation to a more chronic and specific immune response. Th ese cytokines include IFN-alpha, M-CSF, G-CSF, TNF, IL-1, and IL-6. Ou r laboratory and others have shown that neutrophils produce IL-8 in re sponse to LPS or a phagocytic challenge. Although these studies have s hown the induction of IL-8 from polymorphonuclear neutrophils (PMN), r elatively little is known regarding the regulation of PMN-derived IL-8 . Because PMN and monocytes share the same stem cell, and monocyte-der ived IL-8 is regulated by prostaglandin E2 (PGE2), glucocorticoids (de xamethasone; DEX), and the T-Lymphocyte-derived IL-4, we postulated th at PMN-derived IL-8 production may be regulated in a similar manner. T o test this hypothesis, PMN were isolated (> 99% pure) from peripheral blood and cultured in media with 5% FCS in the presence or absence of LPS (10 ng/ml; a concentration of LPS that induced the half-maximal p roduction of PMN-derived IL-8) and in the presence or absence of DEX ( 10(-6) M to 10(-10) M), PGE2 (10(-6) M to 10(-10) M), or IL-4 (100 ng/ ml to 100 pg/ml). PMN-derived IL-8 was measured using a specific sandw ich ELISA. DEX and IL-4 in the presence of LPS were found to inhibit P MN-derived IL-8 in both a dose- and time-dependent fashion. DEX and IL -4 in concentrations of 10(-6) M and 10 ng/ml resulted in maximal inhi bition of LPS-induced PMN-derived IL-8, respectively. Moreover, both D EX and IL-4 administration could be delayed 4 hr post-stimulation with LPS and result in significant suppression of PMN-derived IL-8. Intere stingly, in contrast to the regulation of monocyte-derived IL-8 by PGE 2, PGE2 treatment of PMN failed to inhibit the generation of LPS-induc ed IL-8. Northern blot analysis of steady-state IL-8 mRNA demonstrated that both DEX and IL-4 treatment of PMN resulted in a 40 and 52% redu ction in LPS-stimulated PMN-derived IL-8 mRNA, respectively. These res ults support the notion that the PMN is an active and dynamic particip ant of an inflammatory/immune response through the production of IL-8, and that this generation is susceptible to regulation by the immunomo dulating agents, DEX and IL-4.