Drosophila phagocytosis - still many unknowns under the surface

In mammals, phagocytosis coordinates host defence on two levels: It acts both as an effector of the innate immunity, as well as an initiator of the adaptive immunity. The fruit fly Drosophila melanogaster (D. melanogaster) lacks the adaptive immune response, and the role of Drosophila plasmatocytes, cells that resemble phagocytosing mammalian macrophages, is limited to innate immune responses. During the past years, several studies have shed light on the role of phagocytosis in the Drosophila host defence. At least in some infection models, the systemic production of potent antimicrobial peptides (AMPs) does not completely compensate for the need for cellular immune responses. As a model, Drosophila offers powerful tools for studying phagocytosis including, large-scale RNA interference (RNAi) based in vitro screens that can be combined with classical Drosophila genetics. These kinds of approaches have led to important discoveries related especially to microbial recognition by Drosophila plasmatocytes. Events following initial recognition, however, have remained more elusive. This review summarizes the current knowledge on Drosophila phagocytosis focusing on the most recent advancements in the field, and highlighting the benefits the Drosophila system has to offer for research on phagocytosis.