Expression of interleukin-8 by lipopolysaccharide-stimulated bone marrow- derived mononuclear cells

Abstract

Interleukin-8 (IL-8) is a potent neutrophil chemoattractant, produced by a variety of immune and nonimmune cells in response to exogenous and host- derived inflammatory stimuli. We demonstrate here that a suspension of normal bone marrow mononuclear cells, consisting principally of myeloid precursors, produces IL-8 in response to stimulation with lipopolysaccharide (LPS). IL-8- specific mRNA is rapidly induced, being detected first 30 min after stimulation. IL-8 is detected by enzyme-linked immunosorbent assay within 2 h of stimulation, with steady a increase in its level through 72 h. Further studies demonstrated that LPS could serve as a primary stimulus for the expression of IL-8, since LPS challenge in the presence of cycloheximide resulted in superinduction of bone marrow mononuclear cell-derived IL-8 mRNA. These investigations suggest that the stimulatory effect of LPS is independent of other cytokines such as IL-1β. When compared with LPS, IL-1β proved to be a weak signal for the expression of IL-8 by bone marrow mononuclear cells. In a dose-response study, the maximum stimulatory concentration of IL-1β (300 pg/ml) resulted in the production of 500 pg of IL-8 per 106 cells, whereas 1 μg of LPS resulted in the production of 5.5 ng/106 cells. Although IL-1β was not a particularly potent stimulus for IL- 8 production by bone marrow mononuclear cells, peripheral blood mononuclear cells were highly susceptible to IL-1β challenge. In addition, the potential dependence of LPS-induced marrow-derived IL-8 production on the intermediate synthesis of IL-1β was further investigated. Results of studies assessing kinetics, addition of cycloheximide, and blocking with IL-1β neutralizing antibody were all consistent with the ability of LPS to directly induce bone marrow-derived IL-8 independently of IL-1β. These investigations demonstrate that bone marrow may be a significant source of IL-8 and may play a significant role in acute infectious, inflammatory responses.