The researchers from the University of Massachusetts Medical School (UMMS) have identified a human antibody that may prevent or limit SARS-CoV-2 infection that causes Covid-19 disease.
Antibody discovered by the scientists is a cross-reactive human monoclonal antibody (MAB) to SARS-CoV-2 spike proteins which blocks ACE2 receptor binding on the mucosal tissue of the respiratory tract.
The study has been published in the journal Nature Communications.
The origin of the latest discovery can be traced back to 2004 when the researchers at UMMS developed an IgG monoclonal antibody. This antibody was effective against SARS, which belongs to the same virus family as COVID-19.
Soon after the global spread of SARS-CoV-2, the scientists understood the importance of MAB and started studying its potential of treating the Covid-19 infection.
Old SARS programme was revived by them. They retrieved frozen cells that had been developed 16 years earlier.
They wanted to know if what worked for one virus of the coronavirus family could also work for another, including the latest one.
The researchers found that SARS and the SARS-CoV-2 have 90 per cent things in common. However, they also discovered that monoclonal antibody exhibited no binding to the current coronavirus.
Since the same team had worked on a separate research programme to develop “secretory IgAs (sIgA),”, they started to compare the latest study with their earlier work. “secretory IgAs (sIgA) plays a very important role in immunity on mucosal surfaces.
Antibody was produced with this approach. This antibody had a binding affinity and neutralisation activity.
This antibody was designated MAb362.
“We were excited to learn that antibodies to SARS-CoV-2 are more effective in binding to and neutralising the virus when they are in the sIgA isotype of antibody, compared to the usual circulating IgG antibodies,” said Mark Klempner, a professor of medicine at UMMS.
“In nature, sIgA antibodies coat mucosal surfaces like the respiratory, gastrointestinal infections (GI) and GU tracts, where they are stabilised by the mucous layer on these surfaces. There, they perform the important function of preventing binding of a pathogen to host cells, thus preventing infection,” Klempner said.
Based on these results, the team worked with Celia Schiffer, a professor of biochemistry and her then-graduate student Shurong Hou.
They wanted to have conclusive evidences of the effectiveness of the IgA antibody.
They found MAb362 shared a highly similar framework with MAb 80R, another SARS antibody with a crystal structure in complex with SARS-CoV.
Klempner believes that this unique IgA antibody could potentially be applied through mucosal administration, in combination with other systemically administrated therapeutics for direct mucosal protection.
Some Interesting Facts
- Coronaviruses have a large host ranges and diverse family of viruses.
- The greatest amount of coronavirus diversity is seen in bats.
- SARS-CoV was first identified in 2003. This virus had caused the spread of SARS.
- MERS-CoV was identified in 2012. It was responsible for spreading Middle East respiratory syndrome (MERS)
- The latest SARS-CoV-2 causes COVID-19.
- The acronym SARS stands for severe acute respiratory syndrome.
- COVID-19 and SARS have many similarities and dissimilarities as well.
- Both originated from bat and then jumped to humans via an intermediate animal host.
- Both are spread by respiratory droplets.
- Despite sharing some many common symptoms, there are some subtle differences between COVID-19 and SARS.
IgM, IgG and IgA
- IgM, IgG and IgA are different types of antibodies. They all are Y-shaped immunoglobulins.
- IgM antibodies appear later in COVID-19 than with other viruses
- IgG antibodies can be detected only two weeks after infection.
- IgA antibodies aren’t as good as telling SARS-CoV-2 apart from other human coronaviruses.