Fluoride influences haemocytes functionality in the venus clam Venerupis philippinarum

Invertebrates rely only on innate immunity to cope with foreign, potentially pathogenic microorganisms having entered the organism and haemocytes play a pivotal role in immune responses, as they are involved in phagocytosis, encapsulation, secretion of lectins, cytokines and cytotoxic factors. Therefore, adverse effects on haemocytes can compromise the survival of the organism. In the present study, we analysed the effects of the exposure of haemocytes of the venus clam Venerupis philippinarum to fluoride on cell morphology and functionality. Indeed, the increasing concentration of fluoride in many aquatic ecosystems, as a consequence of human activities, is a matter of great concern and the main negative effect of fluoride are related to its inhibition of metabolic processes, such as glycolysis and protein synthesis. Haemocytes, collected from the adductor muscles, were exposed to NaF (10, 50 and 250 mg/L) in filtered seawater (FSW), for 60 min. We observed a significant (p < 0.01) increase in cell mortality, using the Trypan Blue assay, for all the concentrations used in our experiments. The Neutral Red assay indicated a decrease in the stability of the internal membranes after exposure to 250 mg/L as the dye, usually accumulating inside acid compartments, such as lysosomes, leaks from these compartments into the cytoplasm so that the cells assume a pinkish colour. We also reported a significant (p < 0.01) reduction in the fraction of phagocytosing cells which suggests an effect of fluoride ions on the cytoskeleton or the hampering of the interaction with foreign particles. The observed increase in the cell shape factor in haemocytes exposed to 250 mg/L, indicating a decrease in the capability of haemocytes to assume a spreading morphology, fits the former above hypothesis. Future experiments will be directed to assess further the effects of fluoride on haemocyte functionality.