In contrast, iNOS produces 10–100 times more NO for comparatively long periods of time (hours to days) and, during an infection, its expression is localized in specific tissues and cells.[15, 25] It is the iNOS that has been mainly associated with the host response to viral infections.[22, 27] Because of the high levels of NO that iNOS can produce, regulation of this enzyme is particularly important. This evidence concerns the gene NOS2 and viral infectious disease.