Subset-specific mitochondrial stress and DNA damage shape T cell responses to fever and inflammation

Heat is a cardinal feature of inflammation, yet its impacts on immune cells remain uncertain. We show that moderate-grade fever temperatures (39°C) increased murine CD4 T cell metabolism, proliferation, and inflammatory effector activity while decreasing regulatory T cell suppressive capacity. However, heat-exposed T helper 1 (T_H1) cells selectively developed mitochondrial stress and DNA damage that activated Trp53 and stimulator of interferon genes pathways. Although many T_H1 cells subjected to such temperatures died, surviving T_H1 cells exhibited increased mitochondrial mass and enhanced activity. Electron transport chain complex 1 (ETC1) was rapidly impaired under fever-range temperatures, a phenomenon that was specifically detrimental to T_H1 cells. T_H1 cells with elevated DNA damage and ETC1 signatures were also detected in human chronic inflammation. Thus, fever-relevant temperatures disrupt ETC1 to selectively drive apoptosis or adaptation of T_H1 cells to maintain genomic integrity and enhance effector functions.