Complement component Bf/C2b gene mediates immune responses against Aeromonas hydrophila in grass carp Ctenopharyngodon idella

Abstract The complement system is a significant component of innate immunity. Here, we identified a Bf/C2 homolog ( gcBf/C2b ) in grass carp. gcBf/C2b shares a high similarity with Bf/C2b counterparts in other teleosts. gcBf/C2b transcription was widely distributed in different tissues, induced by Aeromonas hydrophila in vivo and in vitro , and affected by lipopolysaccharide and flagellin stimulation in vitro . In cells over-expressing gcBf/C2b , transcript levels of all components except gcC5 were significantly enhanced, and gcBf/C2b , gcIL1β , gcTNF-α , gcIFN , gcCD59 , gcC5aR1 , and gcITGβ-2 were significantly upregulated after A. hydrophila challenge or stimulation with bacterial pathogen-associated molecular patterns (PAMPs). However, gcBf/C2b in interference cells down-regulated the transcript levels after A. hydrophila challenge, and gcBf/C2b induced NF-κB signaling. These findings indicate the vital role of gcBf/C2b in innate immunity in grass carp.