IL-6 is a pleiotropic cytokine with a broad range of pro- and anti-inflammatory functions that is produced by appropriately stimulated monocytes. However, whether human neutrophils do so, remains still controversial in the literature. To clarify such issue, we explored with additional studies at epigenetic level, whether human neutrophils express IL-6 in response to lipopolysaccharide (LPS), which in autologous monocytes represents a major IL-6 inducer. We found that highly purified (> 99,7 %) neutrophils stimulated at 5 million/ml with 100 ng/ml ultrapure LPS for 24 h released no or very negligible (< 20 pg/ml) amounts of IL-6, unlike autologous monocytes (50 ng/ml/2,5 million/ml). Neutrophils neither expressed IL-6 mRNA or IL-6 primary transcripts at time points (up to 6 h) in which they were maximally produced in autologous monocytes. Consistent with the lack of any IL-6 transcriptional activity, no increase of IL-6 promoter activity could be observed in neutrophils incubated with LPS for 4 h, as revealed by formaldehyde-assisted isolation of regulatory elements (FAIRE). In contrast, a 10-fold increase of nucleosome free DNA levels was detected at the IL-6 promoter of autologous monocytes treated as neutrophils. Furthermore, by chromatin immunprecipitation (ChIP) no H4Ac (an epigenetic marker of transcriptionally active chromatin) was detected at the IL-6 locus (spanning a 30 kb range) of neutrophils incubated with LPS for up to 5 h, in large contrast to monocytes. Taken together, these results suggest that the differential capacity of human neutrophils and monocytes to express IL-6 upon LPS activation is likely controlled by epigenetic mechanisms.
Chromatin configurations correlate with the differential capacity of human neutrophils and monocytes to express IL-6 in response to LPS
Zimmermann, Maili;TAMASSIA, Nicola;CASTELLUCCI, Monica;ROSSATO, Marzia;BAZZONI, Flavia;CASSATELLA, Marco Antonio
2013-01-01
Abstract
IL-6 is a pleiotropic cytokine with a broad range of pro- and anti-inflammatory functions that is produced by appropriately stimulated monocytes. However, whether human neutrophils do so, remains still controversial in the literature. To clarify such issue, we explored with additional studies at epigenetic level, whether human neutrophils express IL-6 in response to lipopolysaccharide (LPS), which in autologous monocytes represents a major IL-6 inducer. We found that highly purified (> 99,7 %) neutrophils stimulated at 5 million/ml with 100 ng/ml ultrapure LPS for 24 h released no or very negligible (< 20 pg/ml) amounts of IL-6, unlike autologous monocytes (50 ng/ml/2,5 million/ml). Neutrophils neither expressed IL-6 mRNA or IL-6 primary transcripts at time points (up to 6 h) in which they were maximally produced in autologous monocytes. Consistent with the lack of any IL-6 transcriptional activity, no increase of IL-6 promoter activity could be observed in neutrophils incubated with LPS for 4 h, as revealed by formaldehyde-assisted isolation of regulatory elements (FAIRE). In contrast, a 10-fold increase of nucleosome free DNA levels was detected at the IL-6 promoter of autologous monocytes treated as neutrophils. Furthermore, by chromatin immunprecipitation (ChIP) no H4Ac (an epigenetic marker of transcriptionally active chromatin) was detected at the IL-6 locus (spanning a 30 kb range) of neutrophils incubated with LPS for up to 5 h, in large contrast to monocytes. Taken together, these results suggest that the differential capacity of human neutrophils and monocytes to express IL-6 upon LPS activation is likely controlled by epigenetic mechanisms.
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