k1: rate constant for reaction with ROS and anti-oxidant IC50: half maximal inhibitory concentration of anti-oxidant Here, to detect a sufficient ESR signal in the neutrophil derived ROS detection system, we used a DMPO concentration that is five times higher than that used in the H2O2/UV system. According to the above relationship, five times higher concentration of LVFX would be needed in the experiment of neutrophil system. In addition to oxidative stress, nitrative stress is also involved in influenza virus-induced lung injuries and mortality. Since the increased production of NO is heavily dependent on the expression of iNOS which, in turn, is induced by IFN-, the presence of a NO synthase inhibitor or the suppression of excessive levels of IFN- could result in the survival of more of the mice. Moreover, compared with wild-type mice, in extracellular SOD transgenic mice, not only IFN- but also NOx levels and lung nitrotyrosine formation induced by a influenza virus infection are inhibited. Therefore, it is conceivable that NO or NOderived species act to enhance influenza-associated pathology. This notion is supported in the literature based on the use of NOS inhibitors during infections with murine cytomegalovirus. These findings point to the importance of the role of the ROS-IFN–NO system in lung injuries in mice that were infected with the influenza virus. The IFN- that is produced by the influenza virus infection model mice is derived from T cells. Kaminski et al. reported that ciprofloxacin, a fluoroquinolone antibiotic, exerts an immunosuppressive effect on human T cells by depleting mtDNA, impairing mitochondrial function, thus resulting in a reduced ROS generation. They also indicated that H2O2-mediated oxidative signals control this gene transcription. Moreover, an SOD mimic inhibits antigen-presenting cell dependent T cell proliferation and IFN- production. Akamatsu et al. reported that ofloxacin exerts an inhibitory effect against O2- derived from neutrophils that had been stimulated by a zymosan treatment. In addition, deferoxamine and DMTU have been reported to inhibit the inflammatory response of endothelial cells by decreasing the levels of NF-B, a regulatory molecule for IL-1, TNF- or IFN-. These findings suggest that the reduction in IFN- caused by the administration of LVFX is partly dependent on its anti-oxidative effect. On the other hand, IFN- derived from cytotoxic CD8 T cells is also important for achieving this amelioration, but Tc1 and Tc2 play different roles. Our findings are different 
from those reported for KO mice, in which LVFX was reported to not completely suppress IFN- production. The over expression of SOD or an 169939-93-9 web erythromycin treatment has been reported to partially suppress IFN- production, which ameliorated influenza PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19736794 virus infections. Susceptibility to bacterial pneumonia is enhanced in influenza virus infections, and the mechanism responsible for this appears to involve the production of excess IFN-. From the standpoint of inhibiting secondary bacterial infections, the suppression of IFN- leads to the restoration of innate immunity against pneumonia. Other mechanisms for regulating the immune system by FQs are known. Cyclic AMP, protein kinase A and Phosphodiesterases, PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19735871 signal molecules or enzymes associated with a series of intracellular protein phosphorylation or transcription factor activation/suppression, are known to be regulated by FQs. The inhibitory effect on TNF- production triggered by
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