An immune response-based approach to evaluate physiological stress in rehabilitating loggerhead sea turtle

The sea turtles maintaining in rescue centres can cause physiological stress to the animals with subsequent effects, such as the imbalance of immune system components. It is therefore crucial to investigate how innate immune responses are influenced by stress within recovery centers with the aim to use them as primary tools for the evaluation of the rescued specimens’ health status and for developing more effective conservative strategies. In this study we monitored for the first time different immune responses in hospitalized Mediterranean loggerhead sea turtles (Caretta caretta) (n = 88), comparing them with free-ranging animals (n = 11). The final scope was to identify sensitive tools based on immune responses parameters that rescue centers operators could use to verify the stress condition of hospitalized specimens. Blood samples were obtained from loggerhead sea turtles hospidalized for different periods (≤2 months; >2 months and ≤1 year; >1 year) in various Italian rescue centers. Free-ranging turtles were captured in the South of Spain during a shipboard survey with a minimal invasive technique. Samples were analyzed for different stress-associated parameters (white cells count, heterophils:lymphocytes (H:L) ratio, respiratory burst, total antioxidant status (TAS), lysozyme). Free-ranging specimens showed lower values for most of the measured parameters. The highest values of TAS, lysozyme activity, respiratory burst and leukocytes profile were detected during the first 2 months of hospitalization, that resulted as the most critical period for the rehabilitation of turtles. After more than 1 year, immune values were similar to the values of free-ranging, indicating an acclimatization to captivity and health conditions amelioration. Moreover, monocytes low levels and eosinophils significant decrease in hospitalized animals indicated the absence of chronic inflammations and reduction of parasitic load during rehabilitation. Statistical analysis pointed out that lysozyme activity and eosinophyls count represent valid methods to diagnose physiological stress and inflammation in hospitalized loggerhead sea turtles.