Water-soluble derivatives of NBT also exist and can be used to measure superoxide production online, as with the ferricytochrome c assay. Detailed protocols for these assays can be found in [14]. Care should be taken with neutrophils derived from shipped blood, in which superoxide derived from damaged mitochondria may lead to a false-positive NBT result

[16]. A number of reagents is known to react with superoxide, to be excited by this process and then to release energy in the form of light (chemiluminescence). Among these are lucigenin (bis-N-methyl-acridinium nitrite) and isoluminol (6-amino-2,3-dihydro-1,4,-phtalazinedione). Talazoparib mw Isoluminol does not pass membranes and therefore detects exclusively extracellular superoxide. For this reaction, addition of a peroxidase to the reaction mixture is required. Chemiluminescence assays are highly sensitive and can HKI-272 therefore be carried out with very few cells. Protocols,

also for microtitre plate assays, can be found in [14, 17]. Hydrogen peroxide (H2O2) has oxidizing properties; such reactions are catalyzed by peroxidases (although these enzymes can also use superoxide as a substrate). Well-known H2O2-detecting agents are dihydrorhodamine-1,2,3 (DHR), 10-acetyl-3,7-dihydroxyphenoxazine (resorufine, Amplex Red) and 5-amino-2,3-dihydro-1,4-phtalazinedione (luminol). DHR enters the cells freely and is oxidized intracellularly to rhodamine-1,2,3, which emits a bright fluorescent signal at 585 nm when excited by light with a wavelength of 488 nm [18-20]. This oxidation reaction is peroxidase-dependent and thus relies upon the activity of myeloperoxidase or eosinophil peroxidase in the phagocytes. In case of myeloperoxidase (MPO) deficiency, a not uncommon condition, the DHR assay with neutrophils will give a negative

result, which may be misinterpreted as an NADPH oxidase deficiency, i.e. as CGD [21]. The assay is carried out in a flow cytometer and thus measures the fluorescent signal from each separate cell, which can again be used for detection of carriers of X-CGD (see section Oxidase activity or protein expression in single cells). Care should be taken to select neutrophils by their scatter characteristics and gate out apoptotic cells to avoid a false bimodal fluorescence pattern that might be mistaken for Amylase a mosaic of oxidase-positive and -negative neutrophils. It is a highly sensitive and reliable assay that can be performed with as little as 0·2 ml of blood. For a detailed protocol, see [14]. Amplex Red does not enter cells and therefore detects only H2O2 excreted by the phagocytes. For this reason, a peroxidase is added to the assay mixture. Amplex Red is oxidized to the brightly fluorescent resorufin, which can be detected at 580 nm after excitation at 530 nm. The assay can be carried out in a microtitre plate on a plate reader with a fluorescence detector.