Difference between revisions of "Neutralisation (immunology)"

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Covering an antigen in antibodies make it less infectious and less pathogenic. In the image on the right, virus entry to the cell is prevented by neutralizing antibodies binding to the virus.

Neutralisation or neutralization or sterilizing immunity in the immunological sense refers to the ability of specific antibodies to block the site(s) on viruses that the latter use to enter target cells. Neutralisation renders the virus no longer infectious (or pathogenic). The surface of viruses contains viral proteins that bind to host cell receptors enabling infection of the host cell. Neutralizing antibodies bind and block the viral surface proteins, preventing host cell entry. After a first encounter by vaccination or natural infection, immunological memory allows for a more rapid production of neutralizing antibodies following the next exposure to the virus.

Vaccines

Vaccines are administered to develop immunity to a virus.[1] An effective vaccine induces the production of antibodies that are able to neutralize the majority of variants of a virus, although virus mutation may cause the need for yearly vaccination.[1] Introducing a weakened form of a virus through vaccination allows for the production of neutralizing antibodies by B cells. After a second exposure, the neutralizing antibody response is more rapid due to the existence of memory B cells that produce antibodies specific to the virus.[1]

Viral infection and antibody response

Viruses cause infection by entering cells and taking over cellular machinery in order to produce copies of themselves.[2] Cell entry is essential in the viral life cycle, as viruses cannot replicate outside of cells and depend on the use of internal components of host cells for replication. Both enveloped and non-enveloped viruses require interaction between viral proteins and cell membrane receptors in order to gain entry into the target cell.[3] Once attached to the cell surface, enveloped and non-enveloped viruses can use a variety of mechanisms for entry. Enveloped viruses have a viral envelope, or outer lipid bilayer membrane that is generated by budding from the virus producer cell; these viruses enter cells when this membrane fuses with the target cell membrane.[2] Non-enveloped viruses can enter cells by forming pores or other breakdowns in integrity of the plasma membrane.[3] Once viruses have entered the cell, they then use a variety of mechanisms to hijack cellular materials and functions to produce viral proteins.  

Antibody production is a critical part of the vertebrate immune response to foreign invaders. Antibodies are proteins that can recognize and bind to specific viral antigens. In B cells, somatic recombination can generate a vast repertoire of different antibodies, each produced by a different B (or plasma) cell – so that a vast array of antigens can be neutralized. Neutralizing antibodies can block at multiple points in a viral entry pathway.[4] Blocking access to cell surface receptors is a common strategy and is often mediated by binding to and neutralizing glycoproteins of enveloped viruses and the protein shell of non-enveloped viruses.[5] Neutralizing antibodies can block infection post-attachment as well. For example, neutralizing antibodies can prevent conformational changes in a viral protein that is required for the virus to enter the cell after attachment to has occurred. In some cases, the virus is unable to infect even after the antibody dissociates.

Virus evasion of neutralizing antibodies

Viruses use a variety of mechanisms to evade neutralizing antibodies.[5] Viral genomes mutate at a high rate. Mutations that allow viruses to evade a neutralizing antibody will be selected for, and hence prevail. Conversely, antibodies also simultaneously evolve by affinity maturation during the course of an immune response, thereby improving recognition of viral particles. Some viruses evolve faster than others, which can require the need for vaccines to be updated in response.[5] This is most exemplified by the vaccine for the influenza virus, which must be updated annually to account for the recent circulating strains of the virus. Conserved parts of viral proteins that play a central role in viral function are less likely to evolve over time, and therefore are more vulnerable to antibody binding. However, viruses have evolved certain mechanisms to steric access of an antibody to these regions, making binding difficult.[5] Viruses with a low density of surface structural proteins are more difficult for antibodies to bind to.[5] “Glycan shields” can also facilitate evasion of neutralizing antibodies. That is, the presence of N- and O- linked glycans may decrease antibody binding affinity to some viral glycoproteins.[5] HIV-1, the cause of human AIDS, uses both of these mechanisms.[6][7]

Treatment with neutralizing antibodies

Broadly neutralizing antibodies (bNAbs) have been researched as a potential treatment for HIV-1 and influenza.[8][9] bNAbs are antibodies that can bind to and block many variants of a virus, and therefore have a heightened efficacy.[10] In the past ten years, much effort has been directed at identifying and testing bNAbs against HIV-1.[11]

References

  1. ^ a b c Burton, Dennis R. (2002). "Antibodies, viruses and vaccines". Nature Reviews Immunology. 2 (9): 706–713. doi:10.1038/nri891. ISSN 1474-1733. PMID 12209139.
  2. ^ a b Cohen, Fredric S. (2016). "How Viruses Invade Cells". Biophysical Journal. 110 (5): 1028–1032. Bibcode:2016BpJ...110.1028C. doi:10.1016/j.bpj.2016.02.006. PMC 4788752. PMID 26958878.
  3. ^ a b Thorley, Jennifer A.; McKeating, Jane A.; Rappoport, Joshua Zachary (2010). "Mechanisms of viral entry: sneaking in the front door". Protoplasma. 244 (1–4): 15–24. doi:10.1007/s00709-010-0152-6. ISSN 0033-183X. PMC 3038234. PMID 20446005.
  4. ^ Corti, Davide; Lanzavecchia, Antonio (2013). "Broadly Neutralizing Antiviral Antibodies". Annual Review of Immunology. 31 (1): 705–742. doi:10.1146/annurev-immunol-032712-095916. ISSN 0732-0582. PMID 23330954.
  5. ^ a b c d e f VanBlargan, Laura A.; Goo, Leslie; Pierson, Theodore C. (2016). "Deconstructing the Antiviral Neutralizing-Antibody Response: Implications for Vaccine Development and Immunity". Microbiology and Molecular Biology Reviews. 80 (4): 989–1010. doi:10.1128/MMBR.00024-15. ISSN 1092-2172. PMC 5116878. PMID 27784796.
  6. ^ Crispin, Max; Ward, Andrew B.; Wilson, Ian A. (2018-05-20). "Structure and Immune Recognition of the HIV Glycan Shield". Annual Review of Biophysics. 47 (1): 499–523. doi:10.1146/annurev-biophys-060414-034156. ISSN 1936-122X. PMC 6163090. PMID 29595997.
  7. ^ Guha, Debjani; Ayyavoo, Velpandi (2013). "Innate Immune Evasion Strategies by Human Immunodeficiency Virus Type 1". Isrn Aids. 2013: 954806. doi:10.1155/2013/954806. ISSN 2090-939X. PMC 3767209. PMID 24052891.
  8. ^ McCoy, Laura E.; Burton, Dennis R. (2017). "Identification and specificity of broadly neutralizing antibodies against HIV". Immunological Reviews. 275 (1): 11–20. doi:10.1111/imr.12484. PMC 5299474. PMID 28133814.
  9. ^ Sok, Devin; Burton, Dennis R. (2018). "Recent progress in broadly neutralizing antibodies to HIV". Nature Immunology. 19 (11): 1179–1188. doi:10.1038/s41590-018-0235-7. ISSN 1529-2908. PMC 6440471. PMID 30333615.
  10. ^ Landais, Elise; Moore, Penny L. (2018). "Development of broadly neutralizing antibodies in HIV-1 infected elite neutralizers". Retrovirology. 15 (1): 61. doi:10.1186/s12977-018-0443-0. ISSN 1742-4690. PMC 6125991. PMID 30185183.
  11. ^ Bhiman, Jinal N.; Lynch, Rebecca M. (2017). "Broadly Neutralizing Antibodies as Treatment: Effects on Virus and Immune System". Current HIV/AIDS Reports. 14 (2): 54–62. doi:10.1007/s11904-017-0352-1. ISSN 1548-3568. PMC 5401706. PMID 28349376.

Notes

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