P2X7 from j774 murine macrophages acts as a scavenger receptor for bacteria but not yeast

Abstract We studied the effects of extracellular ATP and Ca 2+ on uptake of bacteria ( Staphylococcus aureus or Escherichia coli ) and live yeast ( Candida glabrata) by J774 macrophages to determine the role of endogenous P2X7 receptors in phagocytosis. Our findings show that phagocytosis of bio-particles coated with S. aureus or E. coli was blocked by ATP and the P2X7 receptor agonist BzATP, while yeast phagocytosis was not. A438079, an antagonist of P2X7 receptors, partially reverted the effects of ATP on bacterial phagocytosis. To determine if P2X7-mediated Ca 2+ entry into macrophages was blocking the engulfment of bacteria, we measured phagocytic activity in the absence or presence of 2 mM extracellular Ca 2+ with or without ATP. Ca 2+ , in the absence of ATP, was required for engulfment of E. coli and C. glabrata but not S. aureus . Adding ATP inhibited phagocytosis of S. aureus and E. coli regardless of Ca 2+ , suggesting that Ca 2+ entry was not important for inhibiting phagocytosis. On the other hand, phagocytosis of normal or hyper-adherent C. glabrata mutants had an absolute requirement for extracellular Ca 2+ due to yeast adhesion to macrophages mediated by Ca 2+ -dependent adhesion proteins. We conclude that unstimulated P2X7 from J774 cells act as scavenger receptor for the uptake of S. aureus and E. coli but not of yeast; Ca 2+ entry via P2X7 receptors play no role in phagocytosis of S. aureus and E. coli ; while the effect of Ca 2+ on C. glabrata phagocytosis was mediated by the adhesins Epa1, Epa6 and Epa7.