Exposure to benzo(a)pyrene interfered with cell composition and immune ability of common carp (Cyprinus carpio) intestine through inducing cell heterogeneous responses

The intricate heterogeneity of fish intestinal cell types response to environmental stressors has remained largely unaddressed due to previous technological limitations. Emerging single-cell sequencing technology (scRNA-seq), derived from the 2010s, may be a key breakthrough in this area, which could accurately obtain the transcriptome of each cell. In this context, common carp (Cyprinus carpio), which takes the intestine as the main immune organ, was selected as the test subject in this study. The study, mainly based on single-cell sequencing technology and supplemented by gas chromatography mass spectrometry (GC/MS), histological sectioning techniques and transcriptome analysis, revealed the detailed heterogeneity responses of intestinal cells in common carp after benzo(a)pyrene (B[a]P) exposure. Our findings showed a dose-dependent effect on B[a]P accumulation within the common carp intestine as the B[a]P concentration increased. B[a]P exposure led to mucous lamina propria edema and confluent intestinal villi. The high concentration group exhibited uneven and adherent intestinal villi, an abnormal decrease in mucosal epithelial cells, vacuolation, and an anomalously widened base thickness.In the intestinal atlas, an increased proportion of T_cells and a decreased proportion of ECs were identified as the most significant features. These changes primarily affected the intestine by impairing development processes and boosting immunocompetence. A comprehensive analysis of the heterogeneous responses of ECs and T_cells to B [a]P exposure revealed that the lysosome-phagosome pathway, strengthened by the "Lysosome" pathway in the EC1 subset and the "Phagosome" pathway in T_cell 2 subset, might be one of the most critical defense mechanisms within the common carp's intestine. In conclusion, our research presents the first description of the intestinal atlas and the heterogeneous responses in common carp following B[a]P exposure. Our findings enrich the understanding of the impact of polyaromatic hydrocarbons, exemplified by B[a]P, on cyprinidae fish.