Docosahexanoic acid (DHA) is generally present in small amounts, but high concentrations of this essential fatty acid can be found in the nervous system, including photoreceptors, synapses, and brain. Why is there so much of it, and why is it so avidly retained in nervous tissue? Professor Nicolas Bazan examines the role of DHA, thereby revealing the identity of a novel docosanoid, neuroprotectin D1 (NPD1). This molecule is synthesized on demand and has potent bioactivity in inflammatory signaling, and also plays an important role as a sentinel, promoting nerve regeneration and survival.There are clues that NPD1 dysregulation may be a key factor in the onset of Alzheimer’s disease. How is NPD1 affected during the onset of Alzheimer’s? Interestingly, Bazan finds the answer by studying another disease, age-related macular degeneration. In vitro data show that microglial cells are a major target of NPD1, which modulates the survival of these important regulatory cells. Bazan concludes by describing the biochemical pathways of NPD1 synthesis, illustrating how this molecule modulates the balance between inflammation and immunity that is central to the process of aging and degeneration.