Lipid droplets are immune first responders

Tiny sacs of lipids long thought to merely act as floating cellular pantries have an unexpected function, according to a new study ( Science 2020, DOI: 10.1126/science.aay8085 ). The lipid droplets can trap attacking pathogens, luring them with free food and then killing them with antimicrobial proteins. Lipid droplets consist of triacylglycerols and cholesteryl esters wrapped inside membrane sacs. When the cell needs a boost, these lipids can be metabolized by the mitochondria, the cell’s energy-generating organelles. Researchers know that these organelles attract pathogens, but they have generally believed that microbial invaders hijack them for energy. There have been some hints that lipid droplets may play an antibacterial role. To uncover the details of this mechanism, researchers from the University of Barcelona first exposed mice to lipopolysaccharides, bacterial membrane molecules that induce an immune response. Then, they isolated lipid droplets from those animals and uninfected ones and added them to