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Mahesh

25/04/24 07:29 AM IST

New type of host defence against Zika, dengue infections revealed

In News
  • Scientists have identified a novel defence mechanism the human body uses to prevent some viruses from transmitting via non-conventional routes.
What does a virus do inside the body?
  • Most human viruses achieve this by ensuring they are present in bodily fluids that contact the outer environment, and subsequently a new host.
  • Once inside the new host, a virus must be present at the correct location to infect new target cells. Viruses are usually highly selective in the cells they infect.
  • This phenomenon, called tropism, occurs because most viruses have special proteins on their outer surface that make contact with a receptor on the host cell. Any cell-type that makes the receptor can be infected by the virus.
  • For example, the receptor for HIV is a protein called CD4.
  • Only cells that make the CD4 protein, such as T-cells and macrophages, can be infected by HIV.
  • Similarly, SARS-CoV-2 uses a receptor called ACE2.
  • Cells of the respiratory tract and some cardiovascular cells all express ACE2, and are target cells for SARS-CoV-2. HIV can’t infect respiratory cells and SARS-CoV-2 can’t infect T-cells or macrophages.
  • Viral transmission is an outcome of a chase inside the host: between the virus making copies of itself and the immune system trying to destroy the virus and infected cells.
  • The virus must transmit before the immune system beats it or the host dies.
PS receptor
  • One such receptor is for a protein called phosphatidyl serine (PS).
  • The PS protein is usually expressed by dying cells in the body, as a signal to the immune cells to destroy them.
  • The immune cells express the PS receptor and fuse themselves with these cells, quietly destroying them.
  • Viruses hijack this pathway with a process called apoptotic mimicry: by expressing the PS protein on their own surfaces, allowing them to infect the very cells that will destroy them.
  • The WHO’s tweet and its subsequent withdrawal exemplifies the difficulties of studying viral transmission.
  • The problem is especially challenging when we’re studying viruses that can use the PS receptor for entry.
  • Since the PS receptor is expressed by many cells – apart from some cells of the immune system – the virus tends to be present in multiple compartments.
  • Yet the mere presence of a virus in a given compartment wouldn’t guarantee transmission from that route.
  • For example, the Zika virus can be detected in semen, saliva, and breast milk but rarely spreads through these means despite the presence of target cells in the oral and genital cavities.
  • Zika transmits mainly via mosquitoes.
About discovery
  • The discovery of PS-coated vesicles for immunity represents a novel type of host defence against viral infection.
  • While it is too early to speculate on potential therapeutic applications from this discovery, it opens up avenues for further research.
Source- The Hindu

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