Trained immunity can improve the disease resistance of red swamp crayfish (Procambarus clarkii)

Trained immunity has been widely observed in mammals. Its identification in red swamp crayfish (Procambarus clarkii) is important for disease resistance in the crayfish farming industry. In this study, the mortality, expression of immune genes, production of reactive oxygen species (ROS), and phagocytosis ability of haemocytes in crayfish infected by pathogens (Vibrio parahaemolyticus or white spot syndrome virus) and crayfish trained with β-glucan or PBS (the control) were assessed when they were re-challenged by the pathogens. The results showed that the mortality of the trained and re-challenged crayfish were significantly lower than those of the untrained and challenged crayfish. Furthermore, the expression of immune genes, including Resistance (R), ALF, crustin2, and proPO, ROS levels, and phagocytosis ability of haemocytes, was significantly improved in the trained crayfish compared to that in the untrained crayfish. Interestingly, we found that the immune memory of trained crayfish lasted for at least 18 days. Together, these results indicate that crayfish develops trained immunity that can play an important role in the disease resistance. This suggests that trained immunity may be applied to improve disease resistance and crayfish production.