Interleukin-12 increases interleukin-8 production and release by human polymorphonuclear neutrophils

Interleukin (IL) 12 is a heterodimeric cytokine mainly produced by phagocyt es-important target cells for IL-12 in particular with a chemotactic effect -and antigen-presenting cells in response to various microorganisms. Becaus e IL-8 is a strong chemokine for polymorphonuclear neutrophils (PMNs), we i nvestigated the effect of IL-12 on PMN IL-8 production. IL-12 alone had no significant effect, hut with lipopolysaccharide (LPS) it was additive at bo th protein and mRNA levels. Actinomycin D at the beginning of culture inhib ited IL-8 mRNA induction, whereas late addition affected IL-8 transcript st ability, suggesting gene transcription involvement. Results with parthenoli de and tyrphostin AG490 suggest that nuclear factor-kappaB and signal trans ducer and activator of transcription 4 play a role. The IL-12 additive effe ct was restricted to IL-8 release, with no action on cell-associated IL-8. IL-12 additive effects occurred after 18 h of culture, with no marked upreg ulation of IL-12 receptor expression, and were blocked by actinomycin D add ed after 16 h of culture. Tumor necrosis factor (TNF) alpha and interferon (IFN) gamma had intermediate roles; their specific inhibition reduced IL-12 's effect. IL-12's chemotactic mechanism seemed mediated by overproduction and release of IL-8 by human PMNs in the presence of LPS, an effect involvi ng TNF-alpha and IFN-gamma secretion. These results point to a new role for IL-12 in inflammation, through an autocrine amplification loop.