The effect of β-glucan on formation and functionality of neutrophil extracellular traps in carp (Cyprinus carpio L.)

• β-Glucan augments formation of neutrophil extracellular traps in carp head kidney- and kidney-derived neutrophils.
• β-Glucan increases entrapment of Aeromonas hydrophila by carp head kidney- and kidney-derived neutrophils.
• β-Glucan does not stimulate antimicrobial activity of carp head kidney- and kidney-derived neutrophils against Aeromonas hydrophila.

The formation of neutrophil extracellular traps (NETs) has been characterised as a novel antimicrobial host defence strategy of neutrophils besides phagocytosis and degranulation, which may lead to entrapment and subsequent immobilisation and/or killing of bacterial pathogens. Here we studied the effect of the feed additive β-glucan, namely MacroGard®, on the formation and functionality of NETs in carp. Therefore, common carp (Cyprinus carpio) head kidney and kidney cells were isolated and treated with or without β-glucan over time. The formation of NETs was analysed by immunofluorescence microscopy and revealed a distinct increase of NET-formation with β-glucan. Furthermore the subsequent entrapment of Aeromonas hydrophila, an important fish pathogen, was increased after stimulating the cells with β-glucan. However, β-glucan did not lead to a stimulation of antimicrobial activity of neutrophils against A. hydrophila. In conclusion, the data underline the fact that the feed additive β-glucan is able to modulate carp neutrophil functions.