New Delhi: Variation in genes encoding proteins involved in immune responses could be behind why some people remain asymptomatic following SARS-CoV-2 infection. Human leukocyte antigen (HLA) genes encode these proteins used by the immune system in identifying and distinguishing healthy cells in the body from infected ones.
Research has shown at least 20 per cent of Covid-infected do not develop symptoms, or remain asymptomatic.
Also Read: Health Ministry Eases COVID-19 Guidelines For International Travellers
Critical to one’s immunity and highly varied among individuals, the HLA system might have specific variants rendering them more protected against or vulnerable to Covid, the researchers in this US-Australia collaborative study wondered.
Studying asymptomatic infection may improve our understanding of the features of the immune system that promote rapid clearance of the virus, the study published in the journal Nature said.
To understand if an HLA variation might predispose some people to asymptomatic Covid infection, the researchers enrolled 29,947 individuals to participate in a smartphone-based study designed to track COVID-19 symptoms and outcomes. All of them were DNA sequenced for their HLA genetic profiling.
A total of 1,428 unvaccinated individuals reported a positive test for infection with SARS-CoV-2 and 136 of them reported having no symptoms.
Also Read: New Air Monitor Can Detect Covid Variants In About Five Minutes
One in five individuals who remained asymptomatic after infection were found to carry a common variant of HLA called HLA-B*15:01. People carrying two copies of this variant were more than eight times likely to remain asymptomatic than those carrying other versions of HLA, the study found. According to Jill Hollenbach, professor at the University of California San Francisco, US,
We hypothesised that their immune system could react so fast and powerfully that the virus was eliminated before causing any symptoms. It’s like having an army that already knows what to look for and can tell by the uniform that these are the bad guys.
In a separate arm of the study, the researchers found that individuals carrying HLA-B*15:01 with no prior exposure to SARS-CoV-2 had T cells (a type of immune cell) that were reactive to SARS-CoV-2 protein fragments sharing some genetic sequences with other seasonal coronaviruses.
This finding indicated that people carrying HLA-B*15:01 and previously exposed to seasonal cold viruses had pre-existing immunity to SARS-CoV-2 and could rapidly eliminate the virus before symptoms could present.
The researchers analysed this to be because the T cells from pre-pandemic individuals, that could identify viral particles from past coronaviruses, created an immunological memory from the previous coronaviruses.
These memory T cells recognise SARS-CoV-2, owing to its high similarities with those coronaviruses, and kill it very quickly. Danillo Augusto, assistant professor at the University of North Carolina at Charlotte, US, said,
So, even if the bad guys changed the uniform, the army would still be able to identify them by their boots or maybe a tattoo on their arms. That is how our immunological memory works to keep us healthy.
(This story has not been edited by NDTV staff and is published from a syndicated feed.)
NDTV – Dettol have been working towards a clean and healthy India since 2014 via the Banega Swachh India initiative, which is helmed by Campaign Ambassador Amitabh Bachchan. The campaign aims to highlight the inter-dependency of humans and the environment, and of humans on one another with the focus on One Health, One Planet, One Future – Leaving No One Behind. It stresses on the need to take care of, and consider, everyone’s health in India – especially vulnerable communities – the LGBTQ population, indigenous people, India’s different tribes, ethnic and linguistic minorities, people with disabilities, migrants, geographically remote populations, gender and sexual minorities. In wake of the current COVID-19 pandemic, the need for WASH (Water, Sanitation and Hygiene) is reaffirmed as handwashing is one of the ways to prevent Coronavirus infection and other diseases. The campaign will continue to raise awareness on the same along with focussing on the importance of nutrition and healthcare for women and children, fight malnutrition, mental wellbeing, self care, science and health, adolescent health & gender awareness. Along with the health of people, the campaign has realised the need to also take care of the health of the eco-system. Our environment is fragile due to human activity, which is not only over-exploiting available resources, but also generating immense pollution as a result of using and extracting those resources. The imbalance has also led to immense biodiversity loss that has caused one of the biggest threats to human survival – climate change. It has now been described as a “code red for humanity.” The campaign will continue to cover issues like air pollution, waste management, plastic ban, manual scavenging and sanitation workers and menstrual hygiene. Banega Swasth India will also be taking forward the dream of Swasth Bharat, the campaign feels that only a Swachh or clean India where toiletsare used and open defecation free (ODF)status achieved as part of the Swachh Bharat Abhiyan launched by Prime Minister Narendra Modi in 2014, can eradicate diseases like diahorrea and the country can become a Swasth or healthy India.
