Fluoride-Mediated Immune Damage Through Cytokine Network Regulation of Tregs

Long-term fluoride exposure can induce inflammatory responses in various tissues of the body, thereby affecting the inflammatory microenvironment. To explore how fluoride induces changes in immune function within this microenvironment, this study collected baseline information and biological samples from participants in areas with the drinking water type of fluorosis, and simultaneously established Wistar rat models with a 12-week and 24-week fluoride exposure, as well as a 12-week fluoride exposure followed by 12-week pure water feeding regimen. Luminex multiplex assays and enzyme-linked immunosorbent assays (ELISAs) were used to measure cytokine expression levels. Subsequently, correlation analysis, multiple linear regression, and mediation analysis were employed to explore the long-term effects induced by the complex cytokine network during fluoride exposure. The population survey results indicated that fluoride suppressed the expression of pro-inflammatory factors such as Interleukin-2 (IL-2), Interleukin-12 (IL-12), Interferon-γ (IFN-γ), Tumor necrosis factor-α (TNF-α), and anti-inflammatory factors such as Interleukin-4 (IL-4), Interleukin-13 (IL-13), and Interleukin-37 (IL-37), while promoting an increase in the proportion of regulatory T cells (Tregs) in peripheral blood. Among these, IL-2 and IFN-γ mediated the fluoride-induced peripheral Tregs expansion. Animal experiments indicate that the proportion of Tregs in peripheral blood and immune organs increases in a time-dependent manner with fluoride exposure. After reducing the fluoride concentration in the drinking water of rats, the number of Tregs remained significantly elevated. The changes in Treg numbers in the 12-week fluoride feeding group, 24-week fluoride feeding group, and 12-week fluoride feeding followed by 12-week water improvement group were related to the cytokine levels. Therefore, the impact of fluoride on the immune homeostasis has cumulative and long-term effects, and may be related to the accumulation and migration of Tregs induced by fluoride in an inflammatory environment, mediated by cytokines.