P2X7 from j774 murine macrophages acts as a scavenger receptor for bacteria but not yeast
Gabriela Pérez-Flores1, Cesar Hernández-Silva2, Guadalupe Gutiérrez-Escobedo3
1Unidad Académica Multidisciplinaria Zona Huasteca, Universidad Autónoma de San Luis Potosí, Cd. Valles, SLP 79060, Mexico.
Abstract:
We studied the effects of extracellular ATP and Ca2+ 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 Ca2+ entry into macrophages was blocking the engulfment of bacteria, we measured phagocytic activity in the absence or presence of 2 mM extracellular Ca2+ with or without ATP. Ca2+, 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 Ca2+, suggesting that Ca2+ 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 Ca2+ due to yeast adhesion to macrophages mediated by Ca2+-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; Ca2+ entry via P2X7 receptors play no role in phagocytosis of S. aureus and E. coli; while the effect of Ca2+ on C. glabrata phagocytosis was mediated by the adhesins Epa1, Epa6 and Epa7.
Insights
Extracellular ATP and P2X7 receptors inhibit bacterial phagocytosis by macrophages, but not yeast uptake. Calcium ions are crucial for yeast adhesion and engulfment, independent of P2X7 receptors.
Area of Science:
- Immunology
- Cell Biology
- Microbiology
Background:
- Phagocytosis is a key immune mechanism for clearing pathogens.
- P2X7 receptors are involved in immune cell activation and function.
- Extracellular ATP and calcium ions (Ca2+) are critical signaling molecules in cellular processes.
Purpose of the Study:
- To investigate the role of endogenous P2X7 receptors in macrophage phagocytosis of bacteria and yeast.
- To determine the influence of extracellular ATP and Ca2+ on phagocytic activity.
Main Methods:
- Utilized J774 macrophages for phagocytosis assays.
- Studied uptake of Staphylococcus aureus, Escherichia coli, and Candida glabrata.
- Employed P2X7 receptor agonists (BzATP) and antagonists (A438079).
- Manipulated extracellular Ca2+ concentrations and ATP presence.
Main Results:
- Extracellular ATP and BzATP inhibited phagocytosis of S. aureus and E. coli, but not C. glabrata.
- A438079 partially reversed ATP's inhibitory effect on bacterial phagocytosis.
- Ca2+ was essential for E. coli and C. glabrata engulfment, but not S. aureus, in the absence of ATP.
- ATP inhibited bacterial phagocytosis irrespective of Ca2+ levels, indicating Ca2+ entry via P2X7 is not inhibitory.
- Yeast phagocytosis required extracellular Ca2+ due to Ca2+-dependent adhesion mediated by Epa adhesins.
Conclusions:
- Unstimulated P2X7 receptors act as scavenger receptors for S. aureus and E. coli uptake.
- Ca2+ entry through P2X7 receptors does not inhibit bacterial phagocytosis.
- Ca2+ is essential for C. glabrata phagocytosis, mediated by specific yeast adhesins, independent of P2X7 signaling.
