Independent Recognition of Staphylococcus aureus by Two Receptors for Phagocytosis in Drosophila

Integrin beta v, one of two beta subunits of Drosophila integrin, acts as a receptor in the phagocytosis of apoptotic cells. We here examined the involvement of this receptor in defense against infection by Staphylococcus aureus. Flies lacking integrin beta v died earlier than control flies upon a septic but not oral infection with this bacterium. A loss of integrin beta v reduced the phagocytosis of S. aureus and increased bacterial growth in flies. In contrast, the level of mRNA of an antimicrobial peptide produced upon infection was unchanged in integrin beta v-lacking flies. The simultaneous loss of integrin beta v and Draper, another receptor involved in the phagocytosis of S. aureus, brought about a further decrease in the level of phagocytosis and accelerated death of flies compared with the loss of either receptor alone. A strain of S. aureus lacking lipoteichoic acid, a cell wall component serving as a ligand for Draper, was susceptible to integrin beta v-mediated phagocytosis. In contrast, a S. aureus mutant strain that produces small amounts of peptidoglycan was less efficiently phagocytosed by larval hemocytes, and a loss of integrin beta v in hemocytes reduced a difference in the susceptibility to phagocytosis between parental and mutant strains. Furthermore, a series of experiments revealed the binding of integrin beta v to peptidoglycan of S. aureus. Taken together, these results suggested that Draper and integrin beta v cooperate in the phagocytic elimination of S. aureus by recognizing distinct cell wall components, and that this dual recognition system is necessary for the host organism to survive infection.