Abstract
Nile tilapia (Oreochromis niloticus) is an economically important fish worldwide. However, pollutant exposure during culture can make them susceptible to opportunistic pathogens infections, such as Aeromonas hydrophila. In this regard, diazinon (DZN), an organophosphate pesticide (OP), has been reported to exert immunotoxic effects. Therefore, this work aimed to evaluate the pro-inflammatory cytokines expression and the innate immunity mechanisms (phagocytosis and ROS) in leukocytes of O. niloticus pre-exposed to DZN and challenged with inactivated A. hydrophila. Adult male O. niloticus fish were exposed in vivo to 0.97, 1.95, and 3.91 mg/L DZN for 24 h, evaluating the IL-1β and IL-6 expression by RT-PCR. Additionally, phagocytic activity and ROS production (H(2)O(2) and O(2)(−)) were assessed by flow cytometry in DZN-exposed organisms and challenged with A. hydrophila. Data indicate an IL-1β and IL-6 expression increase in DZN-exposed organisms (0.97 mg/L for 24 h). An increase in phagocytic activity was observed in the A. hydrophila-challenged group and the DZN-exposed group. However, in DZN-exposed organisms and A. hydrophila, phagocytosis was decreased. Regarding ROS production, in PMA-stimulated cells, a significant increase was observed in the group challenged with A. hydrophila compared to the control group (without pesticide) and the DZN-exposed group. The data evidence an OP-induced inflammatory response. Furthermore, although the organisms can respond to bacterial stimuli, a decrease in phagocytic parameters is observed in the context of co-exposure to DZN and challenge with A. hydrophila, generating immunosuppression, which could cause infection susceptibility and impact aquaculture production.