Viral apoptotic mimicry

Journal name:
Nature Reviews Microbiology
Year published:
Published online


As opportunistic pathogens, viruses have evolved many elegant strategies to manipulate host cells for infectious entry and replication. Viral apoptotic mimicry, defined by the exposure of phosphatidylserine — a marker for apoptosis — on the pathogen surface, is emerging as a common theme used by enveloped viruses to promote infection. Focusing on the four best described examples (vaccinia virus, dengue virus, Ebola virus and pseudotyped lentivirus), we summarize our current understanding of apoptotic mimicry as a mechanism for virus entry, binding and immune evasion. We also describe recent examples of non-enveloped viruses that use this mimicry strategy, and discuss future directions and how viral apoptotic mimicry could be targeted therapeutically.

At a glance


  1. Classic apoptotic mimicry.
    Figure 1: Classic apoptotic mimicry.

    During classic apoptotic mimicry, a virus acquires host cell phosphatidylserine and incorporates it into the viral membrane. Exposed phosphatidylserine on the viral surface binds directly or indirectly to phosphatidylserine receptors, which facilitate virus entry or infection. Shown are several potential strategies that viruses may use to acquire phosphatidylserine in their membranes during assembly. Ebola virus (EBOV) has been shown to bud from plasma membrane microdomains, or lipid rafts, that are highly enriched for phosphatidylserine in the external leaflet. Furthermore, it has been proposed that vaccinia virus (VACV), which acquires its membrane within the host cytoplasm and exits host cells by inducing cell lysis, derives its membrane from endoplasmic reticulum (ER) sheets generated by the rupture of ER cisternae. Finally, dengue virus (DENV) and other flaviviruses derive their membrane via ER budding. Although these examples cover a range of mechanisms, it is also possible that phosphatidylserine enrichment is facilitated by the viral modulation of lipid flippases or of apoptosis (not illustrated). Recent evidence indicates that phosphatidylserine exposed on the viral surface binds to both direct phosphatidylserine receptors, such as T cell immunoglobulin and mucin receptor (TIM) proteins, and indirect phosphatidylserine receptors, such as AXL and tyrosine protein kinase receptor 3 (TYRO3), which require phosphatidylserine-bridging molecules. Both EBOV and DENV have been shown to use both direct and indirect phosphatidylserine receptors, whereas VACV has only been shown to use the indirect receptor AXL. Whether EBOV and DENV can engage these various receptors simultaneously or whether VACV can use other phosphatidylserine receptors has not been determined. For some viruses, such as EBOV and VACV, engagement of phosphatidylserine receptors triggers their internalization by macropinocytosis. For other viruses, including DENV, binding of phosphatidylserine to receptors on the host cell surface induces clathrin-mediated uptake, which is an alternative mechanism of endocytosis. After internalization, downstream signalling cascades promote additional steps of infection.

  2. Non-classic apoptotic mimicry.
    Figure 2: Non-classic apoptotic mimicry.

    In non-classic apoptotic mimicry, non-enveloped viruses use alternative means to engage phosphatidylserine receptors. For instance, the non-enveloped polyomavirus simian virus 40 (SV40), which exits cells by lysis, mimics the phosphatidylserine-bridging molecule GAS6 to engage tyrosine protein kinase receptor 3 (TYRO3)–AXL–MER (TAM) family receptors. By sharing structural homology with GAS6, the SV40 major structural protein VP1 engages the indirect phosphatidylserine receptor AXL to initiate internalization. Another non-enveloped virus, hepatitis A virus (HAV), probably hijacks phosphatidylserine-containing membranes by budding into cellular organelles known as multivesicular bodies (MVBs). When the MVBs fuse with the plasma membrane, the HAV particles cloaked in the cell-derived envelope are released in a process thought to be akin to exosome egress. The phosphatidylserine-enriched exosome-like particles bind to T cell immunoglobulin and mucin receptor 1 (TIM1) on target cells. To facilitate bulk virus transfer, poliovirus (PV) virions are captured by autophagosome-like double-membrane vesicles. The outer membrane of these vesicles fuses with the cell surface to release phosphatidylserine-rich vesicles containing multiple PV virions. Both PV receptors and phosphatidylserine in these vesicles are required for subsequent infection. However, the phosphatidylserine receptors required remain undefined.

  3. Viral apoptotic mimicry and immune evasion.
    Figure 3: Viral apoptotic mimicry and immune evasion.

    The clearance of apoptotic cells and debris induces an anti-inflammatory response. Binding of apoptotic cells to phosphatidylserine receptors and the subsequent engulfment of these cells by phagocytes initiates the production of anti-inflammatory cytokines such as interleukin-10 (IL-10) and transforming growth factor-β (TGFβ). This initiates a feed-forward suppression of the innate immune response at the level of transcription, and this suppression is dependent on prolonged signalling through signal transducer and activator of transcription (STAT) family proteins. Akin to apoptotic cells, enveloped viruses, including pseudotyped lentivirus vectors and West Nile virus, are thought to use apoptotic mimicry to dampen innate immune responses. Binding of an enveloped virus complexed to bridging molecules (such as GAS6) promotes the activation of tyrosine protein kinase receptor 3 (TYRO3)–AXL–MER (TAM) family receptors, which heterodimerize with type I interferon receptor (IFNAR) to induce suppressor of cytokine signalling 1 (SOCS1) and SOCS3 expression, and this in turn inhibits IFNAR and Toll-like receptor (TLR) signalling. Although phosphatidylserine receptors are often studied individually, it is likely that viruses using apoptotic mimicry can simultaneously engage different phosphatidylserine receptors to modulate various innate immune and anti-inflammatory pathways and thus promote immune evasion. Of note, T cell immunoglobulin and mucin receptor (TIM) family phosphatidylserine receptors are not included in the figure owing to a lack of evidence for their participation in the dampening of immune response by viruses.


  1. Benedict, C. A., Norris, P. S. & Ware, C. F. To kill or be killed: viral evasion of apoptosis. Nat. Immunol. 3, 10131018 (2002).
  2. Poon, I. K., Lucas, C. D., Rossi, A. G. & Ravichandran, K. S. Apoptotic cell clearance: basic biology and therapeutic potential. Nat. Rev. Immunol. 14, 166180 (2014).
  3. Erwig, L. P. & Henson, P. M. Immunological consequences of apoptotic cell phagocytosis. Am. J. Pathol. 171, 28 (2007).
  4. Fadok, V. A., de Cathelineau, A., Daleke, D. L., Henson, P. M. & Bratton, D. L. Loss of phospholipid asymmetry and surface exposure of phosphatidylserine is required for phagocytosis of apoptotic cells by macrophages and fibroblasts. J. Biol. Chem. 276, 10711077 (2001).
  5. Segawa, K. et al. Caspase-mediated cleavage of phospholipid flippase for apoptotic phosphatidylserine exposure. Science 344, 11641168 (2014).
  6. Hochreiter-Hufford, A. & Ravichandran, K. S. Clearing the dead: apoptotic cell sensing, recognition, engulfment, and digestion. Cold Spring Harb. Perspect. Biol. 5, a008748 (2013).
  7. Voll, R. E. et al. Immunosuppressive effects of apoptotic cells. Nature 390, 350351 (1997).
  8. Cvetanovic, M. & Ucker, D. S. Innate immune discrimination of apoptotic cells: repression of proinflammatory macrophage transcription is coupled directly to specific recognition. J. Immunol. 172, 880889 (2004).
  9. Kim, S., Elkon, K. B. & Ma, X. Transcriptional suppression of interleukin-12 gene expression following phagocytosis of apoptotic cells. Immunity 21, 643653 (2004).
  10. Erwig, L. P. & Henson, P. M. Clearance of apoptotic cells by phagocytes. Cell Death Differ. 15, 243250 (2008).
  11. Finnemann, S. C., Bonilha, V. L., Marmorstein, A. D. & Rodriguez-Boulan, E. Phagocytosis of rod outer segments by retinal pigment epithelial cells requires αvβ5 integrin for binding but not for internalization. Proc. Natl Acad. Sci. USA 94, 1293212937 (1997).
  12. Wood, W. et al. Mesenchymal cells engulf and clear apoptotic footplate cells in macrophageless PU.1 null mouse embryos. Development 127, 52455252 (2000).
  13. Vanlandschoot, P. & Leroux-Roels, G. Viral apoptotic mimicry: an immune evasion strategy developed by the hepatitis B virus? Trends Immunol. 24, 144147 (2003).
  14. Bhattacharyya, S. et al. Enveloped viruses disable innate immune responses in dendritic cells by direct activation of TAM receptors. Cell Host Microbe 14, 136147 (2013).
  15. Jemielity, S. et al. TIM-family proteins promote infection of multiple enveloped viruses through virion-associated phosphatidylserine. PLoS Pathog. 9, e1003232 (2013).
  16. Kondratowicz, A. S. et al. T-cell immunoglobulin and mucin domain 1 (TIM-1) is a receptor for Zaire Ebolavirus and Lake Victoria Marburgvirus. Proc. Natl Acad. Sci. USA 108, 84268431 (2011).
  17. Meertens, L. et al. The TIM and TAM families of phosphatidylserine receptors mediate dengue virus entry. Cell Host Microbe 12, 544557 (2012).
  18. Mercer, J. & Helenius, A. Vaccinia virus uses macropinocytosis and apoptotic mimicry to enter host cells. Science 320, 531535 (2008).
  19. Moller-Tank, S., Kondratowicz, A. S., Davey, R. A., Rennert, P. D. & Maury, W. Role of the phosphatidylserine receptor TIM-1 in enveloped-virus entry. J. Virol. 87, 83278341 (2013).
  20. Morizono, K. et al. The soluble serum protein Gas6 bridges virion envelope phosphatidylserine to the TAM receptor tyrosine kinase Axl to mediate viral entry. Cell Host Microbe 9, 286298 (2011).
  21. Shimojima, M., Stroher, U., Ebihara, H., Feldmann, H. & Kawaoka, Y. Identification of cell surface molecules involved in dystroglycan-independent Lassa virus cell entry. J. Virol. 86, 20672078 (2012).
  22. Moller-Tank, S. & Maury, W. Phosphatidylserine receptors: enhancers of enveloped virus entry and infection. Virology 468470, 565580 (2014).
  23. Mazzon, M. & Mercer, J. Lipid interactions during virus entry and infection. Cell. Microbiol. 16, 14931502 (2014).
  24. Mukhopadhyay, S., Kuhn, R. J. & Rossmann, M. G. A structural perspective of the flavivirus life cycle. Nat. Rev. Microbiol. 3, 1322 (2005).
  25. Kay, J. G., Koivusalo, M., Ma, X., Wohland, T. & Grinstein, S. Phosphatidylserine dynamics in cellular membranes. Mol. Biol. Cell 23, 21982212 (2012).
  26. Leventis, P. A. & Grinstein, S. The distribution and function of phosphatidylserine in cellular membranes. Annu. Rev. Biophys. 39, 407427 (2010).
  27. Chlanda, P., Carbajal, M. A., Cyrklaff, M., Griffiths, G. & Krijnse-Locker, J. Membrane rupture generates single open membrane sheets during vaccinia virus assembly. Cell Host Microbe 6, 8190 (2009).
  28. Maruri-Avidal, L., Weisberg, A. S. & Moss, B. Direct formation of vaccinia virus membranes from the endoplasmic reticulum in the absence of the newly characterized L2-interacting protein A30.5. J. Virol. 87, 1231312326 (2013).
  29. Pike, L. J., Han, X., Chung, K. N. & Gross, R. W. Lipid rafts are enriched in arachidonic acid and plasmenylethanolamine and their composition is independent of caveolin-1 expression: a quantitative electrospray ionization/mass spectrometric analysis. Biochemistry 41, 20752088 (2002).
  30. Pike, L. J., Han, X. & Gross, R. W. Epidermal growth factor receptors are localized to lipid rafts that contain a balance of inner and outer leaflet lipids: a shotgun lipidomics study. J. Biol. Chem. 280, 2679626804 (2005).
  31. Soares, M. M., King, S. W. & Thorpe, P. E. Targeting inside-out phosphatidylserine as a therapeutic strategy for viral diseases. Nat. Med. 14, 13571362 (2008).
  32. Zhou, Y., Frey, T. K. & Yang, J. J. Viral calciomics: interplays between Ca2+ and virus. Cell Calcium 46, 117 (2009).
  33. Bratton, D. L. et al. Appearance of phosphatidylserine on apoptotic cells requires calcium-mediated nonspecific flip-flop and is enhanced by loss of the aminophospholipid translocase. J. Biol. Chem. 272, 2615926165 (1997).
  34. Mercer, J., Schelhaas, M. & Helenius, A. Virus entry by endocytosis. Annu. Rev. Biochem. 79, 803833 (2010).
  35. Doherty, G. J. & McMahon, H. T. Mechanisms of endocytosis. Annu. Rev. Biochem. 78, 857902 (2009).
  36. Mercer, J. & Helenius, A. Virus entry by macropinocytosis. Nat. Cell Biol. 11, 510520 (2009).
  37. Mercer, J. & Helenius, A. Gulping rather than sipping: macropinocytosis as a way of virus entry. Curr. Opin. Microbiol. 15, 490499 (2012).
  38. Ichihashi, Y. & Oie, M. The activation of vaccinia virus infectivity by the transfer of phosphatidylserine from the plasma membrane. Virology 130, 306317 (1983).
  39. Laliberte, J. P. & Moss, B. Appraising the apoptotic mimicry model and the role of phospholipids for poxvirus entry. Proc. Natl Acad. Sci. USA 106, 1751717521 (2009).
  40. Frei, A. P. et al. Direct identification of ligand-receptor interactions on living cells and tissues. Nat. Biotech. 30, 9971001 (2012).
  41. Schmidt, F. I., Bleck, C. K., Helenius, A. & Mercer, J. Vaccinia extracellular virions enter cells by macropinocytosis and acid-activated membrane rupture. EMBO J. 30, 36473661 (2011).
  42. Nanbo, A. et al. Ebolavirus is internalized into host cells via macropinocytosis in a viral glycoprotein-dependent manner. PLoS Pathog. 6, e1001121 (2010).
  43. Saeed, M. F., Kolokoltsov, A. A., Albrecht, T. & Davey, R. A. Cellular entry of ebola virus involves uptake by a macropinocytosis-like mechanism and subsequent trafficking through early and late endosomes. PLoS Pathog. 6, e1001110 (2010).
  44. Shimojima, M. et al. Tyro3 family-mediated cell entry of Ebola and Marburg viruses. J. Virol. 80, 1010910116 (2006).
  45. Hunt, C. L., Kolokoltsov, A. A., Davey, R. A. & Maury, W. The Tyro3 receptor kinase Axl enhances macropinocytosis of Zaire ebolavirus. J. Virol. 85, 334347 (2011).
  46. Gould, E. A. & Solomon, T. Pathogenic flaviviruses. Lancet 371, 500509 (2008).
  47. Grove, J. & Marsh, M. The cell biology of receptor-mediated virus entry. J. Cell Biol. 195, 10711082 (2011).
  48. Shimojima, M. & Kawaoka, Y. Cell surface molecules involved in infection mediated by lymphocytic choriomeningitis virus glycoprotein. J. Vet. Med. Sci. 74, 13631366 (2012).
  49. Cao, W. et al. Identification of α-dystroglycan as a receptor for lymphocytic choriomeningitis virus and Lassa fever virus. Science 282, 20792081 (1998).
  50. Jae, L. T. et al. Virus entry. Lassa virus entry requires a trigger-induced receptor switch. Science 344, 15061510 (2014).
  51. Kunz, S. et al. Posttranslational modification of α-dystroglycan, the cellular receptor for arenaviruses, by the glycosyltransferase LARGE is critical for virus binding. J. Virol. 79, 1428214296 (2005).
  52. Morizono, K. & Chen, I. S. Role of phosphatidylserine receptors in enveloped virus infection. J. Virol. 88, 42754290 (2014).
  53. Drayman, N. et al. Pathogens use structural mimicry of native host ligands as a mechanism for host receptor engagement. Cell Host Microbe 14, 6373 (2013).
  54. Kaplan, G. et al. Identification of a surface glycoprotein on African green monkey kidney cells as a receptor for hepatitis A virus. EMBO J. 15, 42824296 (1996).
  55. Feng, Z. et al. A pathogenic picornavirus acquires an envelope by hijacking cellular membranes. Nature 496, 367371 (2013).
  56. Chen, Y. H. et al. Phosphatidylserine vesicles enable efficient en bloc transmission of enteroviruses. Cell 160, 619630 (2015).
  57. Shimojima, M., Ikeda, Y. & Kawaoka, Y. The mechanism of Axl-mediated Ebola virus infection. J. Infect. Dis. 196, S259S263 (2007).
  58. Rothlin, C. V., Ghosh, S., Zuniga, E. I., Oldstone, M. B. & Lemke, G. TAM receptors are pleiotropic inhibitors of the innate immune response. Cell 131, 11241136 (2007).
  59. Nakahashi-Oda, C., Tahara-Hanaoka, S., Honda, S., Shibuya, K. & Shibuya, A. Identification of phosphatidylserine as a ligand for the CD300a immunoreceptor. Biochem. Biophys. Res. Commun. 417, 646650 (2012).
  60. Simhadri, V. R. et al. Human CD300a binds to phosphatidylethanolamine and phosphatidylserine, and modulates the phagocytosis of dead cells. Blood 119, 27992809 (2012).
  61. Nakahashi-Oda, C. et al. Apoptotic cells suppress mast cell inflammatory responses via the CD300a immunoreceptor. J. Exp. Med. 209, 14931503 (2012).
  62. Liu, L. et al. Vaccinia virus induces strong immunoregulatory cytokine production in healthy human epidermal keratinocytes: a novel strategy for immune evasion. J. Virol. 79, 73637370 (2005).
  63. Kinchen, J. M. A model to die for: signaling to apoptotic cell removal in worm, fly and mouse. Apoptosis 15, 9981006 (2010).
  64. Kinchen, J. M. & Ravichandran, K. S. Identification of two evolutionarily conserved genes regulating processing of engulfed apoptotic cells. Nature 464, 778782 (2010).
  65. Kariolis, M. S. et al. An engineered Axl 'decoy receptor' effectively silences the Gas6–Axl signaling axis. Nat. Chem. Biol. 10, 977983 (2014).
  66. Verma, A., Warner, S. L., Vankayalapati, H., Bearss, D. J. & Sharma, S. Targeting Axl and Mer kinases in cancer. Mol. Cancer Ther. 10, 17631773 (2011).
  67. Shibata, T. et al. Axl receptor blockade ameliorates pulmonary pathology resulting from primary viral infection and viral exacerbation of asthma. J. Immunol. 192, 35693581 (2014).
  68. Li, M. et al. TIM-family proteins inhibit HIV-1 release. Proc. Natl Acad. Sci. USA 111, E3699E3707 (2014).
  69. Reed, J. C. Dysregulation of apoptosis in cancer. J. Clin. Oncol. 17, 29412953 (1999).
  70. Fadok, V. A. et al. Exposure of phosphatidylserine on the surface of apoptotic lymphocytes triggers specific recognition and removal by macrophages. J. Immunol. 148, 22072216 (1992).
  71. Borrego, F. The CD300 molecules: an emerging family of regulators of the immune system. Blood 121, 19511960 (2013).
  72. Lemke, G. & Rothlin, C. V. Immunobiology of the TAM receptors. Nat. Rev. Immunol. 8, 327336 (2008).
  73. Hanayama, R. et al. Identification of a factor that links apoptotic cells to phagocytes. Nature 417, 182187 (2002).
  74. Hoffmann, P. R. et al. Phosphatidylserine (PS) induces PS receptor-mediated macropinocytosis and promotes clearance of apoptotic cells. J. Cell Biol. 155, 649659 (2001).
  75. Nakaya, M., Tanaka, M., Okabe, Y., Hanayama, R. & Nagata, S. Opposite effects of rho family GTPases on engulfment of apoptotic cells by macrophages. J. Biol. Chem. 281, 88368842 (2006).
  76. Zhou, Z. & Yu, X. Phagosome maturation during the removal of apoptotic cells: receptors lead the way. Trends Cell Biol. 18, 474485 (2008).
  77. Fadok, V. A. et al. Macrophages that have ingested apoptotic cells in vitro inhibit proinflammatory cytokine production through autocrine/paracrine mechanisms involving TGF-β, PGE2, and PAF. J. Clin. Invest. 101, 890898 (1998).
  78. Birge, R. B. & Ucker, D. S. Innate apoptotic immunity: the calming touch of death. Cell Death Differ. 15, 10961102 (2008).
  79. Moller-Tank, S., Albritton, L. M., Rennert, P. D. & Maury, W. Characterizing functional domains for TIM-mediated enveloped virus entry. J. Virol. 88, 67026713 (2014).
  80. Feigelstock, D., Thompson, P., Mattoo, P. & Kaplan, G. G. Polymorphisms of the hepatitis A virus cellular receptor 1 in African green monkey kidney cells result in antigenic variants that do not react with protective monoclonal antibody 190/4. J. Virol. 72, 62186222 (1998).
  81. Silberstein, E., Dveksler, G. & Kaplan, G. G. Neutralization of hepatitis A virus (HAV) by an immunoadhesin containing the cysteine-rich region of HAV cellular receptor-1. J. Virol. 75, 717725 (2001).

Download references

Author information


  1. Ali Amara is at Institut National de la Santé et de la Recherche Médicale U944 and Centre National de la Recherche Scientifique UMR 7212, Laboratoire de Pathologie et Virologie Moléculaire, Institut Universitaire d'Hématologie, Université Paris Diderot, Sorbonne Paris Cité, Hôpital Saint-Louis, 1 avenue Claude Vellefaux, 75010 Paris, France.

  2. Jason Mercer is at the Medical Research Council Laboratory for Molecular Cell Biology, University College London, Gower Street, London WC1E 6BT, UK.

Competing interests statement

The authors declare no competing interests.

Corresponding authors

Correspondence to:

Author details

  • Ali Amara

    Ali Amara obtained his Ph.D. from the University of Bordeaux, France, and conducted his postdoctoral research at the Pasteur Institute, Paris, France. He is now the Institut National de la Santé et de la Recherche Médicale (INSERM) Research Director of the Biology of Emerging Viruses group in the Saint-Louis Hospital, Paris. His research aims to decipher how viruses enter target cells and how they exploit the host cell machinery to accomplish their infectious life cycle. He currently uses mosquito-borne viruses (dengue virus, yellow fever virus and West Nile virus) as models. Ali Amara's homepage.

  • Jason Mercer

    Jason Mercer obtained his Ph.D. in the laboratory of Paula Traktman at the Medical College of Wisconsin, Milwaukee, USA, and conducted his postdoctoral research in the laboratory of Ari Helenius at ETH Zurich, Switzerland. He is now Associate Professor of Virus Cell Biology in the Medical Research Council Laboratory for Molecular Cell Biology at University College London, UK. His research group focuses on deciphering the complex interactions between poxviruses and their host cells during infection. Jason Mercer's homepage.

Additional data