Study on IL-8 expression in peripheral blood monocytes

Background: Peripheral blood monocytes are important immune effector cells that play a fundamental role in cellular immunity. In addition to their antigen-presenting and phagocytic activities, monocytes/macrophage produce a vast array of regulatory and chemotactic cytokines. Interleukin-8 (IL-8), a potent neutrophil-activating and chemotactic peptide, is produced in large quantities by mononuclear phagocytes and may be an important mediator of local and systemic inflammation. Overexpression by IL-8 of such inflammation may be an important step of tissue injury frequently seen in inflammatory reaction. So it could be hypothesized that the agents which block the production of IL-8 can decrease the inflammatory reaction and tissue injury. To evaluate this, we described the effect of Dexamethasone, PGE₂, Indomethacin and Interferon-γ (IFN-γ) on IL-8 mRNA and protein expression from LPS-stimulated human peripheral blood monocytes (PBMC). Method: PBMC was isolated from healthy volunteers. To evaluate the effect of Dexamethasone, PGE₂ and Indomethacin, these drug were treated for 1 hour before and after LPS stimulation and IFN-γ was only treated 1 hour before the LPS stimulation. Northern blot analysis for IL-8 mRNA and ELISA for immunoreactive IL-8 protein in culture supernatant were performed. We repeated above experiment three times for Northern blot analysis and two times for ELISA and got the same result. Results: 1) Pre- and post-treatment of Dexamethasone suppressed both the LPS stimulated IL-8 mRNA expression and IL-8 protein release in PBMC. 2) IFN-γ pre-treatment suppressed the IL-8 mRNA expression and IL-8 protein release in unstimulated cells. 3) In LPS stimulated cells, IFN-γ suppressed the IL-8 mRNA expression but IL-8 protein release suppression was not observed. 4) PGE₂ and Indomethacin exert no effect on the LPS-stimulated IL-8 mRNA and protein expression in concentration used in this experiment (PGE₂; 10^-6 M, Indomethacin; 10 μM). Conclusion: One of the mechanisms of antiinflammatory action of Dexamethasone can be explained by the suppressing effect of IL-8 production in some extent and by this antiinflammatory effect, dexamethasone can be used to suppress local and systemic inflammation mediated by IL-8.