Imbalance of human CD4⁺ T lymphocyte subsets following atrazine treatment

While being banned in the European Union, the herbicide atrazine (ATR) is still one of the most used herbicides in the world. ATR is classified as an endocrine disruptor, but the immunotoxic effects of ATR may also be due to its direct impact on immune cells. To study the effects of ATR on human T cells, we activated T cells present in PBMCs of 8 healthy donors in the presence of ATR (0.1-100 μM). After 4 days of culture, T cells were stained to evaluate cell growth and phenotype by flow cytometry. The results demonstrated that ATR treatment exerts an antiproliferative activity on CD4⁺ T cells and decreases their activation, including the percentage of cytokine-producing CD4⁺ T cells. Among these, the percentage of interferon (IFN)-γ- and interleukin (IL)-22-producing CD4⁺ T cells decreased within total CD4⁺ T cells. Moreover, IL-4-, IL-10- and IL-17-producing CD4⁺ T cells decreased within cytokine-producing CD4⁺ T cells. Consequently, ATR caused a dose-related decrease in Th1/Th2 ratio. Many of the effects of ATR treatment were quantitatively different in males and females, with more pronounced effects observed in females. tSNE analysis demonstrated that ATR strongly inhibited the differentiation of two subsets of IFN-γ⁺IL-4⁺CD4⁺ T cells from each of the healthy donors tested and promoted greater differentiation of the CD25⁺FoxP3⁺CD4⁺ T cell subset from seven out of the eight healthy donors tested. In conclusion, the study suggests that ATR skews CD4⁺ T cell activation towards Th2, a phenotype that may promote reduced immunosurveillance and increased risk of cancer, as well as Th2-related diseases such as asthma, thereby presenting an environmental and occupation-related risk to human health.