D rosophila Rab 14 mediates phagocytosis in the immune response to S taphylococcus aureus

Summary Drosophila haemocytes are essential for the animal to resist S taphylococcus aureus infections. Phagocytosis is a central component of the haemocyte‐mediated immune response. It involves regulated interaction between the phagocytic and the endocytic compartments. RabGTP ases are pivotal for the membrane trafficking and fusion events, and thus are often targets of intracellular pathogens that subvert phagocytosis. An in vivo screen identified Rab 2 and Rab 14 as candidates for proteins regulating phagosome maturation. Since Rab 14 is often targeted by intracellular pathogens, an understanding of its function during phagocytosis and the overall immune response can give insight into the pathogenesis of intracellular microbes. We generated a D rosophila Rab 14 mutant and characterized the resulting immune defects in animals and specifically in haemocytes in response to an S . aureus infection. Haemocyte based immunofluorescence studies indicate that Rab 14 is recruited to the phagosome and like Rab 7, a well‐characterized regulator of the phagocytic pathway, is essential for progression of phagosome maturation. Rab 14 mutant haemocytes show impaired recruitment of Rab 7 and of a lysosomal marker onto S . aureus phagosomes. The defect in phagocytosis is associated with higher bacterial load and increased susceptibility to S . aureus in the animal.