Phenanthrene Exposure Induces Immune Dysfunction and Metabolic Disruption in Mice

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental pollutants that may impair immune function. However, the immunotoxic mechanisms of PAH exposure remain largely unexplored. The present study was designed as a mechanistic, effect-oriented investigation, in which male C57BL/6J mice were exposed to phenanthrene via intraperitoneal injection for six consecutive weeks. We assessed toxicological effects of phenanthrene exposure in mice through urinary metabolite profiling, hematological and immunological tests, and serum metabolomics. Urinary concentrations of phenanthrene metabolites demonstrated a clear dose-dependent increase across exposure groups, confirming internal accumulation. Relative organ weight analysis revealed significantly elevated kidney and lung weights in all exposed groups compared with controls. Hematological analysis revealed alterations in leukocyte subpopulations. Flow cytometric analysis showed that lymphocyte percentages among splenic cells were significantly decreased in phenanthrene-exposed mice compared with controls, with reductions of 13.74%, 24.92%, and 27.41% in the low-, medium-, and high-dose groups, respectively. The proportions of CD3⁺, CD4⁺, or CD8⁺ T cell subsets within the lymphocyte population remained stable. Notably, a dose-dependent increase in proinflammatory cytokine-producing CD4⁺ T cells was observed. Moreover, exposure to phenanthrene resulted in a dose-dependent decrease in serum IgG concentrations, with levels reduced by 22.2% in the high-dose group compared with controls. Serum metabolomics profiling revealed significant reductions in galactosylglycerol derivatives and quinic acid, alongside elevated phosphatidylserine levels. Moreover, marked increases in glucuronide conjugates suggested activation of phase II detoxification pathways. Lipidomic analysis demonstrated disturbances in phospholipid homeostasis and the accumulation of diacylglycerol and triacylglycerol species. These results provide multiple lines of mechanistic evidence for phenanthrene-induced immune and metabolic perturbations.