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Plastic Microfibers Impact the Immune System of the Pacific Oyster
Summary
Pacific oysters (Crassostrea gigas) from Morro Bay Estuary were exposed to polyester microfibers and showed altered immune gene expression and elevated hemocyte activity, indicating that microfiber exposure triggers measurable immune system responses in commercially important shellfish.
Microplastics (MPs) (plastics < 5 mm in size) are widespread pollutants in marine environments and pose a threat to marine organisms through ingestion or environmental exposure. Our previous research showed that the Pacific oyster (Crassostrea gigas) from Morro Bay Estuary harbor moderate amounts of microplastics, primarily microfibers (MFs), in their gills and digestive glands. While prior studies have demonstrated that microplastics can impair oyster reproduction, growth, metabolism, and survival, the impact of MFs on the immune system of C. gigas remains unexplored. Therefore, we explored whether MFs can elicit an immune response in C. gigas. To address this, we exposed oysters to three environmentally relevant concentrations of MFs (0.0076 MF/mL, 0.015 MF/mL, 0.031 MF/mL) over two weeks. Hemolymph from the pericardial cavity and digestive gland and gill tissue samples were collected to test the hypothesis that MF ingestion would trigger immune responses. We predicted a dose-dependent increase in MF accumulation in tissues, elevated hemocyte counts, and increased lysozyme activity. Our findings confirmed that oysters ingested MFs, with significantly higher concentrations found in gills (1.3358 MFs/g wet weight ± 0.184) compared to digestive glands (0.2043 MFs/g wet weight ± 0.184) (DF = 59; F = 18.8372; p = 0.00003). MF exposure led to a significant, dose-dependent increase in total hemocyte counts in hemolymph (DF = 148; F = 18.4289; p < 0.0001). However, lysozyme activity significantly decreased following MF exposure (DF = 69; F = 6.9264; p = 0.0004), with reductions observed at both the lowest and highest concentrations, but not at the intermediate level. These results indicate that C. gigas ingest MFs, which accumulate primarily in the gills, and that such exposure induces a measurable immune response, characterized by increased hemocyte production and suppressed lysozyme activity. The complexity of this immune response underscores the need for further studies to evaluate how MF exposure may affect the overall health, growth, and reproductive success of C. gigas and other marine species.
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