Effects of perfluorooctanoic acid and nano titanium dioxide on the immune response and energy allocation in Mytilus coruscus.

Perfluorooctanoic acid (PFOA) functions as a surfactant, while nano-titanium dioxide (nano-TiO₂) serves as an antibacterial agent. These substances are extensively utilized in industrial production and, upon release into aquatic environments, pose significant threats to the viability and development of marine organisms. However, research into the effects of PFOA and nano-TiO₂ on the immune functions and cellular energy allocation (CEA) of bivalves remains limited. To investigate the impact of PFOA and nano-TiO₂ on immunity and cellular energy, we exposed Mytilus coruscus individuals to different concentrations of PFOA (2 and 200 μg/L), either alone or in combination with nano-TiO₂ (0.1 mg/L, particle size: 25 nm) for 14 days. We found that the co-exposure to PFOA and nano-TiO₂ had significant interactive effects on multiple immune function parameters of mussels. PFOA and nano-TiO₂ notably reduced the total hemocyte count (THC), esterase activity (EST), mitochondrial number (MN), lysosomal content (LYSO), and cell viability, while concurrently elevating hemocyte mortality (HM) and reactive oxygen species (ROS) levels. Some immune-related genes, such as Tumor Necrosis Factor-alpha (TNF-α) and Myeloid Differentiation Primary Response 88 (MyD88) were downregulated, while others such as Interleukin 17 (IL-17) and Transforming Growth Factor-beta (TGF-β) were upregulated after 14-day exposure to combined pollutant exposure. Furthermore, negative effects on CEA were observed under both individual and combined pollutant stress. Therefore, PFOA and nano-TiO₂ regulate cellular and humoral immunity through the regulation of immune genes as mediators, while simultaneously disrupting cellular energy metabolism. The immunotoxicity of organic and particulate pollutants, and their mixtures, thus poses a significant risk to the immune defense capabilities of mussel populations in polluted coastal environments.