Delta variant spread easily as the molecular mechanisms regulating host immune response were less potent against it.
Evidence suggests that XBB is the most antibody-evasive SARS-CoV-2 variant identified to date.
In the last almost three years, there have been many SARS-CoV-2 (Covid-19) variants across the world. But it was the Delta variant of the coronavirus, most prevalent in India, that could evade our immune system most efficiently.
That is the conclusion of a study by the Hyderabad-based CSIR-Centre for Cellular and Molecular Biology (CCMB).
The CCMB study, by a group led by Dr Krishnan Harshan, in collaboration with another led by Dr Divya Tej Sowpati, tried to understand if hosts, that is, the humans infected by the virus, reacted differently to the different SARS-CoV-2 variants.
They selected five different SARS-CoV-2 variants and studied how the human immune system responded to the variants. The studied variants included Alpha, Delta, and three other variants that emerged before the Alpha variant.
Upon viral infection, the first line of attack by the host’s immune system is by producing certain defence chemicals that break down the viruses. The researchers studied how their production responds to these five variants.
“We infected the human cells in a cell culture system with these different variants of the virus and monitored the production of known immune defence molecules and the activation of signalling pathways associated with them,” said Dixit Tandel, the first author of the study, in a statement.
“We navigated through the hundreds of immune pathways known to us using high throughput sequencing and analysis,” said Dr Nitesh Kumar Singh, one of the researchers.
The study, published in Microbiology Spectrum Journal, found that the immune system could not produce the defence molecules against the Delta variant as effectively as the other variants. While infection due to the other four variants alerted the immune system quickly, the Delta variant could silently replicate in the host cells.
“We have identified that molecular mechanisms regulating the host immune response have not been as potent against the Delta variant of SARS-CoV-2. This also includes the production of interferons, immune molecules often used for antiviral therapies. The study hints at why the Delta variant could spread more easily,” said Dr Harshan, the lead investigator in this work.
He added that the study also helps us understand how viruses evolve with changing effects on human hosts.
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