PHOENIX: Variants in the microglial receptor TREM2 boost the risk for Alzheimer’s disease, but the protein’s exact role remains something of a mystery. Two recent studies shed more light on the factors affecting TREM2. In the March 3 EMBO Molecular Medicine, researchers led by Christian Haass and Michael Ewers at Ludwig-Maximilians University, Munich, reported that levels of a soluble fragment of TREM2 in cerebrospinal fluid change over the course of Alzheimer’s disease, peaking at prodromal stages. Moreover, sTREM2 correlated with markers of neurodegeneration, hinting the two are connected. Meanwhile, researchers led by Gareth Howell at The Jackson Laboratory, Bar Harbor, Maine, uncovered a link between TREM2 and diet. They found that wild-type and AD mice eating chow that mimicked a typical Western diet not only developed neuroinflammation, but also had more TREM2-positive microglia in their brains than did mice on healthier feed. In addition, the AD mouse brains accumulated more amyloid plaque on Western fare. The research appeared in the February 18 Scientific Reports. Both studies strengthen the evidence for TREM2 activity in AD, but whether the protein protects or harms remains up in the air.