Reactive oxygen species (ROS) play a major role in many diseases, as well as the immune system in general. ROS is a double-edged sword: it is an important second messenger, but also a major cause of tissue damage. In systemic sclerosis (SSc), a sever auto-immune disease, we found ROS triggering abnormal cytokine release in dendritic cells (DCs), leading to vascular damage which causes more ROS. I want to find out where in the DC the ROS has its devastating effects by using optogenetics to induce ROS with subcellular precision. This will tell us more about the etiology of systemic sclerosis.