Pro- and anti-inflammatory cytokine expression in carp blood and head kidney leukocytes exposed to cyanotoxin stress – An in vitro study

Cyanotoxins are toxic, secondary metabolites produced by different species of cyanobacteria that are present all over the world in aquatic environments. No data are available about the molecular mechanisms underlying the stress associated with exposure of fish immune cells to low concentrations of cyanotoxins. The purpose of this study was to determine whether the expression of cytokines that underlie immune regulation are changed after incubation of fish leukocytes with pure cyanotoxins: microcystin- LR (MC-LR), anatoxin-a (Antx-a), or an extract containing Antx-a. The study investigated the relative gene expression of four important cytokines, IL-1β, TNF-α, IL-10, and TGF-β, in carp head kidney and blood leukocytes exposed to toxins at concentrations of 0.01 or 0.1 μg/ml for 4 h. The data showed that pure toxins could induce dysregulation of pro-/anti-inflammatory cytokine expression. Expression of cytokine IL-1 β was highly upregulated following Antx-a exposure, whereas MC-LR induced merely moderate reactions. The expression of TNF-α mRNA was significantly suppressed in blood and head kidney cells incubated with toxins at the higher concentration. These results showed that pure toxins dysregulated the expression of pro-inflammatory cytokines IL-1β and TNF-α more promptly than the anti-inflammatory cytokines TGF-β and IL-10. In contrast, the studies demonstrated a clearly downward trend of pro-inflammatory cytokines and an upward trend of anti-inflammatory cytokines in leukocytes exposed to an extract containing defined concentrations of Antx-a. This study suggests that cyanotoxins present in aquatic environments may exert immunotoxic effects by altering the transcription of important mediators of the fish immune system.