I will discuss our work on the phagocyte NADPH oxdase (NOX2). This crucial multi-subunit complex generates reactive oxygen species (ROS) to kill pathogens but is also essential for immune regulation. We have described EROS as a crucial chaperone for NOX2 assembly and inflammasome signalling. I will present some published work and unpublished findings on EROS’s role in adaptive immunity and a novel regulator of reactive oxygen species generation. I will then describe how investigating the Duox2-Duoxa2 system in ROS generation led us to discover an essential role of thyroid hormone in NK cell biology. This is a collaboration with Alice Denton (Imperial College).