Immunomodulation and apoptotic events in the clam Tapes philippinarum after exposure to 4-nonylphenol

Nonylphenol (NP) is used in the production of nonylphenol ethoxylates (NPEs), NP phosphites and insecticide sprays. NPEs are a large group of nonionic surfactants employed in plastics, latex paints, lubricating oils, emulsifiers, household and industrial detergents and paper and textile industries, whereas NP phosphites are commonly used as stabilisers and antioxidant agents in both rubber and plastic industries. NP is known to be an endocrine disruptor, being able to alter hormonal functions in various aquatic organisms. In this study, specimens of the clam Tapes philippinarum were exposed for 7 days to various sublethal NP concentrations (0, 0+acetone, 0.025, 0.05, 0.1 and 0.2 mg/l) and their effects on the uptake of the vital dye Neutral Red (as index of cell membrane alteration), superoxide dismutase (SOD) and lysozyme activities, the number and volume of haemocytes were evaluated. The capability of NP to induce apoptotic events in haemocytes was also studied. Exposure of clams to 0.2 mg/l NP increased significantly (P<0.05) Neutral Red uptake when compared with controls, suggesting that NP may cause alterations in cell membrane stability. Significant (P<0.01) decreases with respect to controls in both SOD and lysozyme activities were observed at concentration higher than 0.05 mg /l NP. A significant (P<0.001) increase in apoptotic index (i.e., the percentage of haemocytes showing positivity to the TUNEL reaction) was also recorded in the same 54 concentration range. Apoptotic haemocytes generally showed a shrinkage of cell volume and a spherical shape. Alterations in both circulating haemocyte number and volume, consequent to NP exposure, were recorded using a Coulter counter. In this case, we observed both significant increases (P<0.05, for clams exposed to 0.2 mg /l NP) in total number of circulating haemocytes and different size frequency distribution. Our results, showing a relationship between NP exposure and alterations in functional responses of haemocytes, demonstrated that NP can influence immune responses in T. philippinarum.