Antioxidant defenses in the coelomic fluid of Echinometra lucunter (Linnaeus, 1758) stimulated with bacterial inoculums

Phagocytosis is a first-line cellular response mediated by specialized cells denominated coelomocytes- amoebocytes. This process allows for the inclusion of extraneous particles or microorganisms, which are eliminated by the production of reactive oxygen species (ROS). In order to evaluate the antioxidant defense system in the coelomic fluid (CF) of E. lucunter under elevated phagocytic activity (PA), three bacterial strains were inoculated separately, via peristomial membrane: E. coli, V. parahaemolyticus and M. lysodeikticus. The phagocytic capacity (PC), catalase (CAT) and superoxide dismutase (SOD) activities, levels of lipoperoxidation (LPO), sulphydryl groups (-SH) and proteins were determined at 16 h post-injection. In addition, the time of righting response of each individual was noted. The PA, CAT, and proteins showed increments in the organisms inoculated with bacteria. The LPO, SOD, and -SH levels showed no variations among the experimental organisms. The time of righting response showed slight variations in the bacteria-stimulated organisms, as well as a low percentage of lost and reduced movements of their spines and tube feet. The PA and proteins in CF of E. lucunter show the effectiveness of the immune system in the presence of microbial stimulants. Results indicate that CAT plays a preponderant role in the CF to avoid changes in the antioxidant status, associated with the respiratory burst during elevated phagocytic activities. Antioxidant responses of E. lucunter immunostimulated by bacteria may guarantee their survival in their natural habitat.