Peroxiredoxins are important for the regulation of hydrogen peroxide concentrations in ticks and tick cell line.

Ticks are obligate hematophagous ectoparasites, as they need to feed blood from vertebrate hosts for development. Host blood contains high levels of iron. Host-derived iron may lead to high levels of reactive oxygen species (ROS), including hydrogen peroxide (H2 O2 ). Since a high concentration of H2 O2 causes serious damage to organisms, this molecule is known to be a harmful chemical compound for aerobic organisms. On the other hand, the transparent method is compatible with chemical fluorescent probes. Therefore, we tried to establish the visualizing method for H2 O2 in unfed tick tissues. The combination method of a chemical fluorescent probe (BES-H2 O2 -Ac) with the transparent method, Scale, demonstrated in unfed tick tissues that H2 O2 and paraquat could induce oxidative stress in the tissues, such as the midgut and ovary. In addition, an H2 O2 detection method using BES-H2 O2 -Ac was established in Ixodes scapularis embryo-derived cell line (ISE6) in vitro to evaluate the antioxidant activity of peroxiredoxins (PRXs), H2 O2 scavenging enzymes, against H2 O2 in the cells. The effects of paraquat in ISE6 cells were also observed in the PRXs gene-silenced ISE6 cells. A high intensity of H2 O2 fluorescence induced by paraquat was observed in the PRX gene-knockdowned cells. These results suggest that H2 O2 and paraquat act as an H2 O2 inducer, and PRX genes are important for the regulation of the H2 O2 concentration in unfed ticks and ISE6 cells. Therefore, this study contributes to the search for H2 O2 visualization in ticks and tick cell line and furthers understanding of the tick's oxidative stress induced by H2 O2 .