Environmental Low-Dose Radiation Activates Th1 Immunity through the Mitochondria-STING Pathway

The presence of low-dose radiation (LDR) in the environment has become more prevalent. However, the effect of LDR exposure on the immune system remains elusive. Here, we interestingly found that LDR specifically elevated the percentage of CD4⁺IFNγ⁺ Th1 splenocytes, both in vitro and in vivo, without affecting the percentage of CD8⁺IFNγ⁺ Tc1 cells and regulatory T cells. A similar phenomenon was found in T cells from peripheral blood. Mechanistically, we found that LDR can induce mitochondrial damage, which stimulated the STING signaling pathway, leading to the enhanced expression of T-bet, the master transcriptional factor of Th1-cell differentiation. The specific STING signal inhibitor can abrogate the effect of LDR on Th1 differentiation, confirming the central role of the STING pathway. To further validate the immunoregulatory role of LDR, we exposed mice with whole body LDR and evaluated if LDR could protect mice against triple-negative breast cancer through enhanced antitumor immunity. As expected, LDR significantly delayed tumor development and promoted cell death. Meanwhile, LDR resulted in increased tumor-infiltrating Th1 cells, while the proportion of Tc1 and Treg cells remained unchanged. Furthermore, the infiltration of antitumor macrophages was also increased. In summary, we revealed that environmental LDR could specifically regulate Th1 T-cell activities, providing critical information for the potential application of LDR in both clinical and nonclinical settings.