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Nucleotides released by apoptotic cells act as a find-me signal to promote phagocytic clearance


Phagocytic removal of apoptotic cells occurs efficiently in vivo such that even in tissues with significant apoptosis, very few apoptotic cells are detectable1. This is thought to be due to the release of ‘find-me’ signals by apoptotic cells that recruit motile phagocytes such as monocytes, macrophages and dendritic cells, leading to the prompt clearance of the dying cells2. However, the identity and in vivo relevance of such find-me signals are not well understood. Here, through several lines of evidence, we identify extracellular nucleotides as a critical apoptotic cell find-me signal. We demonstrate the caspase-dependent release of ATP and UTP (in equimolar quantities) during the early stages of apoptosis by primary thymocytes and cell lines. Purified nucleotides at these concentrations were sufficient to induce monocyte recruitment comparable to that of apoptotic cell supernatants. Enzymatic removal of ATP and UTP (by apyrase or the expression of ectopic CD39) abrogated the ability of apoptotic cell supernatants to recruit monocytes in vitro and in vivo. We then identified the ATP/UTP receptor P2Y2 as a critical sensor of nucleotides released by apoptotic cells using RNA interference-mediated depletion studies in monocytes, and macrophages from P2Y2-null mice3. The relevance of nucleotides in apoptotic cell clearance in vivo was revealed by two approaches. First, in a murine air-pouch model, apoptotic cell supernatants induced a threefold greater recruitment of monocytes and macrophages than supernatants from healthy cells did; this recruitment was abolished by depletion of nucleotides and was significantly decreased in P2Y2-/- (also known as P2ry2-/-) mice. Second, clearance of apoptotic thymocytes was significantly impaired by either depletion of nucleotides or interference with P2Y receptor function (by pharmacological inhibition or in P2Y2-/- mice). These results identify nucleotides as a critical find-me cue released by apoptotic cells to promote P2Y2-dependent recruitment of phagocytes, and provide evidence for a clear relationship between a find-me signal and efficient corpse clearance in vivo.

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Figure 1: Chemotactic factor released by apoptotic cells attracts monocytes in vitro and in vivo.
Figure 2: Regulated release of ATP and UTP as chemoattractants by apoptotic cells.
Figure 3: P2Y 2 receptor on monocytes and macrophages as a sensor of ATP and UTP released by apoptotic cells.
Figure 4: Interference with the nucleotide find-me signal or its sensing impairs the clearance of apoptotic cells in the thymus.


  1. Henson, P. M. & Hume, D. A. Apoptotic cell removal in development and tissue homeostasis. Trends Immunol. 27, 244–250 (2006)

    Article  CAS  Google Scholar 

  2. Lauber, K., Blumenthal, S. G., Waibel, M. & Wesselborg, S. Clearance of apoptotic cells: getting rid of the corpses. Mol. Cell 14, 277–287 (2004)

    Article  CAS  Google Scholar 

  3. Homolya, L., Watt, W. C., Lazarowski, E. R., Koller, B. H. & Boucher, R. C. Nucleotide-regulated calcium signaling in lung fibroblasts and epithelial cells from normal and P2Y2 receptor (-/-) mice. J. Biol. Chem. 274, 26454–26460 (1999)

    Article  CAS  Google Scholar 

  4. Hogquist, K. A., Baldwin, T. A. & Jameson, S. C. Central tolerance: learning self-control in the thymus. Nature Rev. Immunol. 5, 772–782 (2005)

    Article  CAS  Google Scholar 

  5. Surh, C. D. & Sprent, J. T-cell apoptosis detected in situ during positive and negative selection in the thymus. Nature 372, 100–103 (1994)

    Article  ADS  CAS  Google Scholar 

  6. Ravichandran, K. S. & Lorenz, U. Engulfment of apoptotic cells: signals for a good meal. Nature Rev. Immunol. 7, 964–974 (2007)

    Article  CAS  Google Scholar 

  7. Kadl, A., Galkina, E. & Leitinger, N. Induction of CCR2-dependent macrophage accumulation by oxidized phospholipids in the air-pouch model of inflammation. Arthritis Rheum. 60, 1362–1371 (2009)

    Article  Google Scholar 

  8. Huynh, M. L., Fadok, V. A. & Henson, P. M. Phosphatidylserine-dependent ingestion of apoptotic cells promotes TGF-β1 secretion and the resolution of inflammation. J. Clin. Invest. 109, 41–50 (2002)

    Article  CAS  Google Scholar 

  9. Savill, J., Dransfield, I., Gregory, C. & Haslett, C. A blast from the past: clearance of apoptotic cells regulates immune responses. Nature Rev. Immunol. 2, 965–975 (2002)

    Article  CAS  Google Scholar 

  10. Lauber, K. et al. Apoptotic cells induce migration of phagocytes via caspase-3-mediated release of a lipid attraction signal. Cell 113, 717–730 (2003)

    Article  CAS  Google Scholar 

  11. Truman, L. A. et al. CX3CL1/fractalkine is released from apoptotic lymphocytes to stimulate macrophage chemotaxis. Blood 112, 5026–5036 (2008)

    Article  CAS  Google Scholar 

  12. Mizumoto, N. et al. CD39 is the dominant Langerhans cell-associated ecto-NTPDase: modulatory roles in inflammation and immune responsiveness. Nature Med. 8, 358–365 (2002)

    Article  CAS  Google Scholar 

  13. Chen, Y. et al. ATP release guides neutrophil chemotaxis via P2Y2 and A3 receptors. Science 314, 1792–1795 (2006)

    Article  ADS  CAS  Google Scholar 

  14. Lazarowski, E. R., Homolya, L., Boucher, R. C. & Harden, T. K. Direct demonstration of mechanically induced release of cellular UTP and its implication for uridine nucleotide receptor activation. J. Biol. Chem. 272, 24348–24354 (1997)

    Article  CAS  Google Scholar 

  15. Myrtek, D. & Idzko, M. Chemotactic activity of extracellular nucleotideson human immune cells. Purinergic Signal. 3, 5–11 (2007)

    Article  CAS  Google Scholar 

  16. Burnstock, G. & Knight, G. E. Cellular distribution and functions of P2 receptor subtypes in different systems. Int. Rev. Cytol. 240, 31–304 (2004)

    Article  CAS  Google Scholar 

  17. Moore, D. J. et al. Expression pattern of human P2Y receptor subtypes: a quantitative reverse transcription-polymerase chain reaction study. Biochim. Biophys. Acta 1521, 107–119 (2001)

    Article  CAS  Google Scholar 

  18. Idzko, M. et al. Characterization of the biological activities of uridine diphosphate in human dendritic cells: influence on chemotaxis and CXCL8 release. J. Cell. Physiol. 201, 286–293 (2004)

    Article  CAS  Google Scholar 

  19. Koizumi, S. et al. UDP acting at P2Y6 receptors is a mediator of microglial phagocytosis. Nature 446, 1091–1095 (2007)

    Article  ADS  CAS  Google Scholar 

  20. Hasko, G., Linden, J., Cronstein, B. & Pacher, P. Adenosine receptors: therapeutic aspects for inflammatory and immune diseases. Nature Rev. Drug Discov. 7, 759–770 (2008)

    Article  CAS  Google Scholar 

  21. Kawane, K. et al. Impaired thymic development in mouse embryos deficient in apoptotic DNA degradation. Nature Immunol. 4, 138–144 (2003)

    Article  CAS  Google Scholar 

  22. Hoeppner, D. J., Hengartner, M. O. & Schnabel, R. Engulfment genes cooperate with ced-3 to promote cell death in Caenorhabditis elegans . Nature 412, 202–206 (2001)

    Article  ADS  CAS  Google Scholar 

  23. Reddien, P. W., Cameron, S. & Horvitz, H. R. Phagocytosis promotes programmed cell death in C. elegans . Nature 412, 198–202 (2001)

    Article  ADS  CAS  Google Scholar 

  24. Monks, J., Smith-Steinhart, C., Kruk, E. R., Fadok, V. A. & Henson, P. M. Epithelial cells remove apoptotic epithelial cells during post-lactation involution of the mouse mammary gland. Biol. Reprod. 78, 586–594 (2008)

    Article  CAS  Google Scholar 

  25. Kono, H. & Rock, K. L. How dying cells alert the immune system to danger. Nature Rev. Immunol. 8, 279–289 (2008)

    Article  CAS  Google Scholar 

  26. la Sala, A. et al. Alerting and tuning the immune response by extracellular nucleotides. J. Leukoc. Biol. 73, 339–343 (2003)

    Article  CAS  Google Scholar 

  27. Bournazou, I. et al. Apoptotic human cells inhibit migration of granulocytes via release of lactoferrin. J. Clin. Invest. 119, 20–32 (2009)

    CAS  PubMed  Google Scholar 

  28. Lysiak, J. J., Turner, S. D. & Turner, T. T. Molecular pathway of germ cell apoptosis following ischemia/reperfusion of the rat testis. Biol. Reprod. 63, 1465–1472 (2000)

    Article  CAS  Google Scholar 

  29. Lazarowski, E. R., Boucher, R. C. & Harden, T. K. Constitutive release of ATP and evidence for major contribution of ecto-nucleotide pyrophosphatase and nucleoside diphosphokinase to extracellular nucleotide concentrations. J. Biol. Chem. 275, 31061–31068 (2000)

    Article  CAS  Google Scholar 

  30. Lazarowski, E. R. & Harden, T. K. Quantitation of extracellular UTP using a sensitive enzymatic assay. Br. J. Pharmacol. 127, 1272–1278 (1999)

    Article  CAS  Google Scholar 

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We thank K. Rock, C. Borowski and members of the Ravichandran laboratory for helpful suggestions; I. Juncadella for lung epithelial cells; K. Lauber and S. Wesselborg for providing MCF-7/caspase-3 cells; and R. Tacke for assistance with primary monocyte experiments. This work was supported by Public Health Service grants from the National Institutes of Health (to K.S.R. and N.L.), the American Cancer Society (to M.R.E.) and the University of Virginia Farrow Fellowship (to M.R.E.).

Author Contributions M.R.E. designed, performed and analysed most of the experiments in this study, with input from K.S.R. ATP quantification experiments were performed by F.B.C., and P.T.C. assisted with in vivo thymic apoptosis experiments. E.R.L. performed the high-performance liquid chromatography analysis of supernatants. S.F.W. generated the CD39 expression plasmid and stable Jurkat cell lines. D.P. conducted phagocytosis experiments. A.K. and N.L. performed the mass spectrometry analysis and provided critical support in establishing the air-pouch model system. R.I.W. and J.J.L. conducted immunohistochemical detection of apoptotic cells in the thymus. M.O. and P.S. assisted with the BMDM generation and macrophage chemotaxis experiments. T.K.H. provided critical intellectual input in the preparation of the manuscript. K.S.R. provided overall coordination with respect to conception, design and supervision of the study. K.S.R. and M.R.E. wrote the manuscript with comments from co-authors.

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Correspondence to Kodi S. Ravichandran.

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Elliott, M., Chekeni, F., Trampont, P. et al. Nucleotides released by apoptotic cells act as a find-me signal to promote phagocytic clearance. Nature 461, 282–286 (2009).

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