Final answer:
A negative Nitroblue tetrazolium (NBT) test suggests a deficiency in NADPH oxidase, an enzyme critical for generating reactive oxygen species as part of the immune response.
Step-by-step explanation:
A negative Nitroblue tetrazolium (NBT) test is indicative of a deficiency in the enzyme NADPH oxidase. This enzyme is part of the immune system's mechanism for fighting infections. When activated neutrophils or phagocytes encounter pathogens, they generate reactive oxygen species (ROS) through a process known as the 'respiratory burst.' The ROS are toxic to the invading microbes. The respiratory burst is driven by the enzyme NADPH oxidase, which is involved in the production of superoxide radicals (•O2-) from oxygen using electrons from NADPH. Therefore, a negative NBT test, which measures the ability of cells to reduce the dye Nitroblue Tetrazolium to formazan, suggests that the cells are not producing superoxide and thus are likely deficient in NADPH oxidase.