TAG: GS 3: SCIENCE AND TECHNOLOGY
THE CONTEXT: Recent research conducted at the Institute of Molecular Virology at Ulm University Medical Centre, Germany, sheds light on a novel defense mechanism employed by the human body to inhibit viral transmission via non-conventional routes.
EXPLANATION:
- Published in Nature Microbiology, the study reveals the role of extracellular vesicles in bodily fluids, such as saliva and semen, in inhibiting viral infection.
Extracellular Vesicles as Defense Agents
- Extracellular vesicles, small structures enclosed by fat, play a crucial role in intercellular communication and substance transport.
- The researchers found that these vesicles are abundant in saliva and semen and contain PS proteins on their surfaces, similar to those exploited by viruses for entry.
- Through a series of experiments, they demonstrated that these vesicles compete with viruses for entry receptors, thereby impeding viral infection.
Implications of the Discovery
- The study’s findings extend beyond Zika virus to encompass other viruses that utilize the PS receptor for entry, including dengue, chikungunya, West Nile, ebola, and vesicular stomatitis viruses.
- Importantly, viruses that do not utilize the PS receptor, such as HIV and SARS-CoV-2, remain unaffected by the presence of extracellular vesicles.
- This discovery represents a significant advancement in our understanding of host defense mechanisms against viral infections.
Viruses:
- Viruses, such as Zika, dengue, and chikungunya, are adept at transmitting themselves from host to host, a crucial aspect of their life cycle.
- Achieving successful transmission is a complex interplay between the virus and the host’s immune system.
- For a virus to successfully infect a new host, it must first gain access to target cells, a process known as tropism.
- Tropism is driven by specific interactions between viral surface proteins and receptors on host cells.
- These receptors are typically highly selective, dictating which cells the virus can infect.
- For instance, HIV targets cells expressing the CD4 protein, while SARS-CoV-2 uses the ACE2 receptor for entry.
- One such receptor of interest is phosphatidyl serine (PS), typically expressed by dying cells in the body.
- PS acts as a signal for immune cells to initiate the clearance of these dying cells.
- However, viruses have evolved a strategy known as apoptotic mimicry, wherein they express PS on their own surfaces.
- By doing so, viruses can exploit the PS pathway to infect host cells, effectively hijacking the immune response for their benefit.
Challenges in Studying Viral Transmission
- Studying viral transmission presents significant challenges, particularly when viruses utilize receptors like PS for entry.
- These receptors are often expressed by various cell types, complicating the understanding of transmission routes.
- Additionally, the mere presence of a virus in a bodily fluid does not guarantee transmission through that route.
- For example, although Zika virus can be detected in saliva, semen, and breast milk, it primarily spreads via mosquitoes rather than orally or sexually.
Future Directions and Speculations
- While the therapeutic implications of this discovery are yet to be fully realized, it opens up new avenues for research into potential antiviral strategies.
- Furthermore, the study raises intriguing questions about the evolutionary dynamics between viruses and their hosts.
- The notion that PS-containing vesicles in humans may have influenced the evolution of mosquito-borne viruses presents a thought-provoking avenue for further investigation.