Copyright © 2020 JoVE Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License jove.com June 2020 • 160 • e60983 • Page 1 of 16 Assessing the Age-Specific Phagocytic Ability of Adult Drosophila melanogaster Hemocytes using an In Vivo Phagocytosis Assay Shonda M. Campbell 1 , Michelle Starz-Gaiano 1 , Jeff Leips 1 1 Department of Biology, University of Maryland Baltimore County Corresponding Author Jeff Leips leips@umbc.edu Citation Campbell, S.M., Starz-Gaiano, M., Leips, J. Assessing the Age-Specific Phagocytic Ability of Adult Drosophila melanogaster Hemocytes using an In Vivo Phagocytosis Assay. J. Vis. Exp. (160), e60983, doi:10.3791/60983 (2020). Date Published June 11, 2020 DOI 10.3791/60983 URL jove.com/video/60983 Abstract Phagocytosis is an essential function of the innate immune response. This process is carried out by phagocytic hemocytes whose primary function is to recognize a wide range of particles and destroy microbial pathogens. As organisms age, this process begins to decline, yet little is known about the underlying mechanisms or the genetic basis of immunosenescence. Here, an injection based in vivo phagocytosis assay is used to assess age related changes in different aspects of phagocytosis, such as binding, engulfment, and degradation of internalized particles, by quantifying phagocytic events in hemocytes in adult Drosophila. Drosophila melanogaster has become an ideal model to investigate age related changes in innate immune function for many reasons. For one, many genetic components and functions of the innate immune response, including phagocytosis, are evolutionarily conserved between Drosophila and mammals. Because of that, results obtained from using this protocol are likely to be widely relevant to understanding the age related changes in immune function in a variety of organisms. Additionally, we note that this method provides quantitative estimates of hemocyte phagocytic ability, which could be useful for a variety of research topics, and need not be limited to studies of aging. Introduction The innate immune system, which consists of physical and chemical barriers to infection as well as cellular components, is evolutionary conserved across multicellular organisms 1,2 . As the first line of defense, the innate immune system plays a critical role in combating invading pathogens in all animals 1,2,3 . The components of the innate immune response include a wide range of cell types which are classified on the basis that they lack specificity and immunological memory 2,3,4 . In humans, these cell types include phagocytic monocytes and macrophages, neutrophils, and cytotoxic natural killer cells 4,5 . While having a functional immune system is imperative for host survival, it is clear that the function of immune cells declines with age, a phenomenon known as immunosenescence 5,6 . Being able