RESUMO
Interleukin (IL) 12 is a heterodimeric cytokine mainly produced by phagocytes-important target cells for IL-12 in particular with a chemotactic effect-and antigen-presenting cells in response to various microorganisms. Because IL-8 is a strong chemokine for polymorphonuclear neutrophils (PMNs), we investigated the effect of IL-12 on PMN IL-8 production. IL-12 alone had no significant effect, but with lipopolysaccharide (LPS) it was additive at both protein and mRNA levels. Actinomycin D at the beginning of culture inhibited IL-8 mRNA induction, whereas late addition affected IL-8 transcript stability, suggesting gene transcription involvement. Results with parthenolide and tyrphostin AG490 suggest that nuclear factor-kappaB and signal transducer and activator of transcription 4 play a role. The IL-12 additive effect 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 up-regulation of IL-12 receptor expression, and were blocked by actinomycin D added 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 involving TNF-alpha and IFN-gamma secretion. These results point to a new role for IL-12 in inflammation, through an autocrine amplification loop.