The P2X7-nonmuscle myosin membrane complex regulates phagocytosis of nonopsonized particles and bacteria by a pathway attenuated by extracellular ATP.

Phagocytosis of nonopsonized bacteria is central to innate immunity, but its regulation is less defined. We show that overexpression of the P2X(7) receptor greatly augments the phagocytosis of nonopsonized beads and heat-killed bacteria by transfected HEK-293 cells, whereas blocking P2X(7) expression by siRNA significantly reduces the phagocytic ability of human monocytic cells. An intact P2X(7)-nonmuscle myosin complex is required for phagocytosis of nonopsonized beads because activation of P2X(7) receptors by adenosine triphosphate (ATP), which dissociates myosin IIA from the P2X(7) complex, inhibits this phagocytic pathway. Fresh human monocytes rapidly phagocytosed live and heat-killed Staphylococcus aureus and Escherichia coli in the absence of serum, but the uptake was reduced by prior incubation with ATP, or P2X(7) monoclonal antibody, or recombinant P2X(7) extracellular domain. Injection of beads or bacteria into the peritoneal cavity of mice resulted in their brisk phagocytosis by macrophages, but injection of ATP before particles markedly decreased this uptake. These data demonstrate a novel pathway of phagocytosis of nonopsonized particles and bacteria, which operate in vivo and require an intact P2X(7)-nonmuscle myosin IIA membrane complex. The inhibitory effect of ATP on particle uptake by the macrophage is regulated by the P2X(7) receptor and defines this phagocytic pathway.