Regulation of Il-10 gene expression by Il-6 via Stat3 in grass carp head kidney leucocytes.

Abstract

Interleukin (IL)-10 is a critical anti-inflammatory and late cytokine being produced after the proinflammatory mediators while IL-6 is a promptly synthesized cytokine in response to inflammation in mammals. This chronological expression of interleukin (Il)-6 and Il-10 was also found in grass carp head kidney leucocytes (HKLs) treated by heat-killed Aeromonas hydrophila, supporting the possible interplay between grass carp (gc)Il-6 and gcIl-10 in HKLs. Our further findings were in agreement with this hypothesis that recombinant gcIl-6 (rgcIl-6) promptly and transiently increased gcil10 mRNA levels in grass carp HKLs. Moreover, rgcIl-6 enhanced its own mRNA level and this self-enhancement of gcil6 mRNA level could be partially blocked by rgcIl-10. These results collectively suggest that gcIl-10 production stimulated by gcIl-6 may provide a negative feedback to gcIl-6 production. Interestingly, rgcIl-6 significantly decreased gcil10 mRNA levels in grass carp HKLs after the treatment for 12 and 24h in contrast to its enhancement of gcil10 levels after the treatment for 3h. Involvement of Stat3 but not MEK, p38 MAPK or JNK pathway in the increase of gcil10 mRNA levels by rgcIl-6 was revealed by using the signaling pathway inhibitors. This was supported by the fact that rgcIl-6 stimulated Stat3 phosphorylation in grass carp HKLs. Furthermore, rgcIl-6 had no effect on the stability of gcil10 mRNA after the treatment for 3 to 36h while it increased gcil10 promoter activity after the treatment for 24h. Taken these data together, gcIl-6 can stimulate Il-10 production at early stage but subsequently inhibit il10 mRNA expression in grass carp HKLs, shedding light on the dynamic regulation of il10 mRNA expression by Il-6 in fish immune cells.