Mitochondrial reactive oxygen is critical for IL-12/IL-18-induced IFN-γ production by CD4+ T cells and is regulated by Fas/FasL signaling

Mitochondrial activation and the production of mitochondrial reactive oxygen species (mROS) are crucial for CD4(+) T cell responses and have a role in naive cell signaling after TCR activation. However, little is known about mROS role in TCR-independent signaling and in recall responses. Here, we found that mROS are required for IL-12 plus IL-18-driven production of IFN-gamma, an essential cytokine for inflammatory and autoimmune disease development. Compared to TCR stimulation, which induced similar levels of mROS in naive and memory-like cells, IL-12/IL-18 showed faster and augmented mROS production in memory-like cells. mROS inhibition significantly downregulated IFN-gamma and CD44 expression, suggesting a direct mROS effect on memory-like T cell function. The mechanism that promotes IFN-gamma production after IL-12/IL-18 challenge depended on the effect of mROS on optimal activation of downstream signaling pathways, leading to STAT4 and NF-kappa B activation. To relate our findings to IFN-gamma-driven lupus-like disease, we used Fas-deficient memory-like CD4(+) T cells from lpr mice. Importantly, we found significantly increased IFN-gamma and mROS production in lpr compared with parental cells. Treatment of WT cells with FasL significantly reduced mROS production and the activation of signaling events leading to IFN-gamma. Moreover, Fas deficiency was associated with increased mitochondrial levels of cytochrome C and caspase-3 compared with WT memory-like cells. mROS inhibition significantly reduced the population of disease-associated lpr CD44(hi)CD62L(lo)CD4(+) T cells and their IFN-gamma production. Overall, these findings uncovered a previously unidentified role of Fas/FasL interaction in regulating mROS production by memory-like T cells. This apoptosis-independent Fas activity might contribute to the accumulation of CD44(hi)CD62L(lo)CD4(+) T cells that produce increased IFN-gamma levels in lpr mice. Overall, our findings pinpoint mROS as central regulators of TCR-independent signaling, and support mROS pharmacological targeting to control aberrant immune responses in autoimmune-like disease.