Flow-cytometric Detection of Low-level Reactive Oxygen Species in Cell Lines and Primary Immune Cells

Depending on its concentration and cellular origin the production of reactive oxygen species (ROS) in the organism serves a variety of functions. While high concentrations during an oxidative burst are used to fight pathogens, low to moderate amounts of ROS act as signaling molecules important for several physiological processes such as regulation of immune responses. The ROS-sensitive dye 2',7'-dichlorodihydrofluorescein diacetate (H₂DCFDA) is an inexpensive and well-established tool for measuring intracellular ROS levels. However, it needs to be carefully controlled to be able to draw firm conclusions on the nature of ROS species produced and the cellular source of ROS generation such as the enzyme complex NADPH-oxidase 2 (NOX-2). In this protocol, a robust method to determine low intracellular ROS production using H₂DCFDA was validated by several ROS-specific as well as NOX-2-specific inhibitors. Cells were treated with inhibitors or control substances prior to treatment with the ROS-inducer of interest. H₂DCFDA was added only for the last 30 min of the treatment schedule. To terminate its conversion, we used a ROS-specific inhibitor until analysis by flow cytometry within the FITC-channel (Ex: 488 nm/Em: 519 nm). In summary, this protocol allows the detection of signaling-relevant intracellular ROS production in cell lines and primary immune cells (e.g., Mono Mac 6 cells and Bone marrow-derived dendritic cells, respectively). Using this method in combination with specific inhibitors, we were able to validate even exceptionally low amounts of ROS produced by NOX-2 and relevant for immune-regulatory signaling.