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Type I IFN is a major player in innate and adaptive immune responses. Besides, it is involved in organogenesis and tumor development. Generally, IFN responses are amplified by an autocrine loop with IFN-beta as the priming cytokine. However, due to the lack of sensitive detection systems, where and how type I IFN is produced in vivo is still poorly understood. In this study, we describe a luciferase reporter mouse, which allows tracking of IFN-beta gene induction in vivo. Using this reporter mouse, we reveal strong tissue-specific induction of IFN-beta following infection with influenza or La Crosse virus. Importantly, this reporter mouse also allowed us to visualize that IFN-beta is expressed constitutively in several tissues. As suggested before, low amounts of constitutively produced IFN might maintain immune cells in an activated state ready for a timely response to pathogens. Interestingly, thymic epithelial cells were the major source of IFN-beta under noninflammatory conditions. This relatively high constitutive expression was controlled by the NF Aire and might influence induction of tolerance or T cell development.
Lienenklaus et al. (Mon,) studied this question.