The Meteorin-like cytokine is upregulated in grass carp after infection with Aeromonas hydrophila

Meteorin-like (Metrnl) is a novel immune regulatory factor or adipokine which is mainly produced by activated macrophages. In teleost fish, two homologs are present. In this study, monoclonal antibodies were prepared against recombinant grass carp (Ctenopharyngodon idella, Ci) Metrnl-a in mice and characterized by Western blotting, flow cytometry and immunofluorescent microscopy. In grass carp infected with Aeromonus hydrophila (A. hydrophila), the cells expressing CiMetrnl-a markedly increased in the gills, head kidney and intestine. In the inflamed intestine caused by A. hydrophila infection, the CiMetrnl-a producing cells were detected mainly in the mucosal layer of anterior, middle and posterior segments. Consistently, qRT-PCR analysis showed that the mRNA expression of CiMetrnl-a was markedly induced. Our results suggest that CiMetrnl-a is involved in regulating intestine inflammation caused by bacterial infection.

Automated summary

Monoclonal antibodies against grass carp Metrnl-a were prepared and characterized in this study. The expression of CiMetrnl-a increased in grass carp infected with A. hydrophila, particularly in the gills, head kidney and intestine. CiMetrnl-a producing cells were mainly detected in the mucosal layer of the inflamed intestine caused by A. hydrophila infection. qRT-PCR analysis confirmed the marked induction of CiMetrnl-a mRNA expression. These findings suggest the involvement of CiMetrnl-a in regulating bacterial infection-induced intestine inflammation.