Dr. Maxfield has applied quantitative imaging methods to the study of membrane biology. He was among the first to use fluorescence microscopy for quantitative analysis of membrane traffic, which led to fundamental mechanistic insights regarding the endocytic trafficking of proteins and lipids. This included the initial demonstration that endosomes are acidic and that acidification is essential for many endosomal functions. His laboratory also provided much of the initial characterization of a novel organelle, the endocytic recycling compartment. Using cell culture models, he has shown that microglia can internalize plaque material, but they fail to digest it efficiently because they don’t properly acidify their lysosomes. His laboratory now is extending these studies into in vivo measurements of lysosome acidification and digestion of amyloid plaques by microglia.