6PPD impairs immune responses and fin regeneration in zebrafish

N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), a commonly used antioxidant in tire manufacturing, has been widely detected in the environment and shown to exhibit acute toxicity in several organs. However, the effects of 6PPD on immune responses, particularly following injury, remain poorly understood. In this study, we investigated the impact of 6PPD exposure on immune responses using zebrafish as a model. 6PPD exposure disrupted caudal fin regeneration at various stages of the regenerative process. Further analysis revealed that 6PPD impaired immune responses following fin amputation, as evidenced by the reduced number of lyz⁺/mpx⁺ neutrophils and the downregulation of key immune-related genes. Besides, the morphology of neutrophils was changed upon 6PPD exposure, indicating the defective migration of immune cells. The incubation of zebrafish larvae with lipopolysaccharide (LPS), which induces global immune responses, also exhibited impaired immune function when combined with 6PPD exposure. Additionally, the injection of LPS into the egg yolk or trunk exacerbated immune responses at the injury site, yet 6PPD exposure significantly reduced neutrophil accumulation and downregulated the expression of immune-related genes, confirming the toxicity of 6PPD in immune responses. These findings provide new insights into the toxic effects of 6PPD on immune responses during injury, highlighting its potential to impair immune function in animals and human.