IFNα enhances the production of IL-6 by human neutrophils activated via TLR8

Purpose: Recently, we reported that human neutrophils produce biologically active amounts of IL-6 when incubated with agonists activating TLR8, a receptor recognizing viral single strand RNA. Herein, is investigated the effect of IFNα, a potent antiviral cytokine, on IL-6 production. Methods: Human neutrophils isolated from whole blood of healthy donors or systemic lupus erythematosus (SLE) patients by immunomagnetic beads (99.7 ± 0.2 % purity), were incubated for up to 20 h with or without R848 (a TLR8 agonists), in the presence or the absence of IFNα. Cytokine production and mRNA expression were then measured by ELISA and RT-qPCR, respectively, while analysis of C/EBPβ recruitment at the IL-6 genomic locus was investigated by chromatin immunoprecipitation assays. Results: In this study, data demonstrate that IFNα potently enhances the production of IL-6 in neutrophils stimulated with R848. Such an effect is not caused by an IFNα-dependent induction of TLR7, another receptor for R848, but, rather, it is substantially mediated by an increased release of endogenous TNFα. The latter cytokine, in an autocrine manner, leads to an augmented synthesis of the IκBζ co-activator and an enhanced recruitment of the C/EBPβ transcription factor to the IL-6 promoter. Moreover, data demonstrate that neutrophils from active SLE patients, thus displaying an IFN-induced gene expression signature, produce increased amounts of both IL-6 and TNFα in response to R848 as compared to healthy donors. Discussion: TLR8 ligands, IFNα and TNFα, three players often coexisting in many diseases of viral or autoimmune origin, promote a strong production of IL-6 in human neutrophils, placing this cell type among potential targets for immunotherapeutic interventions. Conclusions: Altogether, data clarify the molecular bases of the IFNα-dependent enhancement of IL-6 production in TLR8-activated neutrophil