Mitochondrial oxidative stress drives IL-12/IL-18-induced IFN-gamma production by CD4+ T cells and is controlled by Fas

Mitochondrial activation and mROS production are crucial for CD4+ T cell responses and have a role in naive cell signaling after TCR activation. However, little is known about their role in recall responses driven by cytokine signaling. Here, we found that mROS are required for IL-12 plus IL-18-driven production of IFN-{gamma}, an essential cytokine in inflammatory and autoimmune disease development. In particular, memory-like cells obtained after activation-induced differentiation showed faster and augmented mROS accumulation and increased IFN-{gamma} production in response to IL-12 plus IL-18 compared to naive T cells. In contrast, mROS induction was similar in naive and memory-like cells after TCR-dependent signaling. Taken together these results suggested that memory-like CD4+ T cells treated by IL-12 plus IL-18 attained conditions for an extraordinary mROS-producing potential. mROS inhibition significantly downregulated the production of IFN-{gamma} and the expression of CD44 activation marker, suggesting a direct mROS effect on the activation of memory-like T cells. Mechanistically, mROS was required for optimal activation of key signaling pathways that drive IFN-{gamma} production after IL-12 plus IL-18 T cell stimulation, such as PKC-{theta}, AKT and STAT4 phosphorylation, and NF-{kappa}B activation. Notably, we identified increased mROS as key promoters of hyperactivation and IFN-{gamma} overproduction in Fas-deficient lpr memory-like CD4+ T cells compared to WT cells, following IL-12 plus IL-18 stimulation. mROS inhibition significantly reduced the population of disease-associated CD44hiCD62Llo lpr CD4+ T cells and their IFN-{gamma} production. These findings uncover a previously unidentified role for Fas in regulating mitochondrial ROS production by memory-like T cells. This apoptosis-independent Fas activity might contribute to the accumulation of CD44hiCD62Llo 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.