Chronic inflammation underlies the pathological progression of various diseases, and thus many efforts have been made to quantitatively evaluate the inflammatory status of the diseases. In this study, we generated a highly sensitive inflammation-monitoring mouse system using a bacterial artificial chromosome (BAC) clone containing extended flanking sequences of the human interleukin 6 gene (hIL6) locus, in which the luciferase (Luc) reporter gene is integrated (hIL6-BAC-Luc). We successfully monitored lipopolysaccharide-induced systemic inflammation in various tissues of the hIL6-BAC-Luc mice using an in vivo bioluminescence imaging system. When two chronic inflammatory disease models, i.e., a genetic model of atopic dermatitis and a model of experimental autoimmune encephalomyelitis (EAE), were applied to the hIL6-BAC-Luc mice, luciferase bioluminescence was specifically detected in the atopic skin lesion and central nervous system, respectively. Moreover, the Luc activities correlated well with the disease severity. Nrf2 is a master transcription factor that regulates antioxidative and detoxification enzyme genes. Upon EAE induction, the Nrf2-deficient mice crossed with the hIL6-BAC-Luc mice exhibited enhanced neurological symptoms concomitantly with robust luciferase luminescence in the neuronal tissue. Thus, whole-body in vivo monitoring using the hIL6-BAC-Luc transgenic system (WIM-6 system) provides a new and powerful diagnostic tool for real-time in vivo monitoring of inflammatory status in multiple different disease models. E xposure to environmental xenobiotics and the accompanying production of cellular oxidative stress give rise to a wide variety of inflammatory diseases in modern society (reviewed in references 1 and 2). To take a step against the widespread prevalence of inflammation-related diseases or low-grade systemic inflammations, it is crucial to elucidate the mechanistic basis for the cellular response to the inflammation. In this aspect, development of an in vivo monitoring system for evaluation of inflammatory status and validation of therapeutic agents has been eagerly awaited. Accurate and sensitive inflammation-monitoring animal models will accelerate further study of inflammatory diseases and development of new therapeutics.Inflammatory stimuli induce gene expression of a series of proinflammatory cytokines, such as tumor necrosis factor (TNF), interleukin 1 (IL-1), and IL-6. Among the proinflammatory cytokines, IL-6 is a key cytokine that is produced by many types of cells, including immune cells (e.g., macrophages and T and B lymphocytes), hepatocytes, glial cells, and fibroblasts (reviewed in reference 3). Expression of IL-6 in resting immune cells is usually suppressed, while it is rapidly induced upon exposure to a variety of inflammatory stimuli (reviewed in reference 4). Subsequently, the induced IL-6 participates in multiple physiological and pathological processes, including innate and acquired immune responses and pathogenesis of autoimmune inflammatory diseases. This sensi...