The coronavirus SARS-CoV-2 could latch extra simply onto the airway cells of individuals with sort A blood in contrast with these with sort B or O blood, a brand new research suggests. The findings trace at a doable rationalization for why, all through the pandemic, research have discovered these with sort A blood are likelier to catch COVID-19 and develop extreme signs than different blood varieties.
Laboratory experiments revealed that a part of the coronavirus referred to as the “receptor binding area” (RBD), which immediately binds to cells to jumpstart an infection, additionally grabs onto distinctive molecules related to sort A blood. These molecules, referred to as antigens, present up on cells that line the respiratory tract, together with the lungs, in response to the research, printed March 3 within the journal Blood Advances.
In concept, binding to those constructions could assist the coronavirus enter and infect the airway cells extra simply — nevertheless, we do not know that for certain but, the research authors advised Reside Science.
“Does this actually affect the flexibility of the virus to get into cells? Does it simply affect its potential to stick to the cells?” stated research writer Dr. Sean Stowell, a transfusion drugs physician-scientist with appointments at Brigham and Girls’s Hospital in Massachusetts and Emory College in Georgia. “That is open-ended. We’re engaged on that proper now, however the jury continues to be out.”
In different phrases, the info present the primary bodily hyperlink between the coronavirus and kind A blood, however extra analysis is required to verify that this distinction impacts the percentages of precise an infection.
Why would blood sort matter?
Because the early days of the pandemic, a number of research of coronavirus sufferers have uncovered developments in what blood varieties appear to turn out to be contaminated most frequently, Reside Science beforehand reported.
“Many research have discovered associations between blood teams and propensity for SARS-CoV-2 infections,” specifically, exhibiting that folks with sort O blood have a decrease threat of catching COVID-19, in contrast with non-O blood varieties, stated Dr. Torben Barington, a medical immunologist at Odense College Hospital and the College of Southern Denmark, who was not concerned within the research. Individuals with sort A blood may additionally be extra prone to develop extreme signs and respiratory failure once they do contract the virus, some research discovered.
“A number of hypotheses have been proposed for these associations, however we nonetheless have to be taught what the mechanisms truly are,” Barington advised Reside Science in an e-mail. This new research hints at a doable rationalization for why SARS-CoV-2 could infect blood sort A people extra simply than sort O — although it would not clarify why sort B can also be linked to extra infections than sort O, he famous.
Stowell stated that he and his colleagues had been curious concerning the hyperlink between blood sort and COVID-19, however that they really struck inspiration for his or her new research whereas growing a diagnostic check for the illness.
Whereas creating the check, “we began taking a look at totally different elements of the virus and realized that the receptor binding area … it seems similar to an historic group of proteins referred to as galectins,” Stowell stated.
Galectins might be present in all multicellular animals and bind to carbohydrates, or sugar constructions, referred to as glycans; in people, galectins might be discovered all around the physique and take part in lots of processes, from muscle improvement to metabolism to immune cell habits, Stowell stated.
Prior to now, “we have noticed that galectins actually like to bind to blood group antigens,” proteins and molecules which are particular to totally different blood teams and stick off the floor of cells. Blood group antigens are available in two flavors — A and B — and the presence or absence of those antigens decide an individual’s blood group — A, B, AB, which has each, or O, which has neither, in response to the American Pink Cross. The antigens are discovered not solely on blood cells within the physique, but additionally on different tissues, together with the liner of the lungs.
Given the molecular similarity between the coronavirus RBD and galectins, “we thought, ‘Properly, perhaps the virus immediately binds to blood group antigens,'” Stowell stated. If that had been the case, blood group antigens could by some means affect the probability of the an infection taking maintain, he stated. For instance, some viruses accrue on cells by first grabbing maintain of glycans on their surfaces, in response to a 2016 report within the journal Present Opinion in Structural Biology; the viruses then let go of those glycans to slide by way of close by entryways into the cell, triggering an infection.
One thing related may probably be taking place with blood group antigens and SARS-CoV-2, the authors thought. With this speculation in hand, the group headed to the lab to run experiments.
Within the lab
The group analyzed how the RBD interacted with crimson blood cells remoted from blood group A, B and O people; additionally they ran experiments with artificial blood group antigens, based mostly on antigens discovered on each respiratory and crimson blood cells from the three blood teams. This allowed the group to check whether or not and the way the RBD binds with blood group antigens on blood cells and within the respiratory tracts.
“The flavour of blood group antigens which are expressed on the floor of crimson blood cells are barely totally different than the flavour that traces our lungs,” Stowell famous. Particularly, as a consequence of their differing molecular constructions, the antigens bind slightly in another way to respiratory cells than they do to blood cells, he stated.
What’s attention-grabbing is that this refined distinction appears to matter to the RBD of the coronavirus, he stated. Primarily based on the experiments, the RBD would not readily bind to any of the crimson blood cell antigens and exhibits no choice between the blood varieties, on this regard. In distinction, the RBD “exhibited excessive choice” for the kind A antigens discovered on respiratory cells.
“It was clear; there was this choice. We did not anticipate that,” Stowell stated. Now, “whether or not that really implies that the virus is extra prone to infect blood group A, I would say, we do not know.”
On condition that these information had been drawn from lab experiments, the consequence could not completely replicate what occurs within the human physique, stated Fumiichiro Yamamoto, an immunohematologist on the Josep Carreras Leukaemia Analysis Institute in Barcelona, who was not concerned within the research.
“The binding could or could not replicate the precise scenario on the cell floor,” particularly for the reason that density of antigens on the cell floor could differ from situations examined within the lab experiments, Yamamoto advised Reside Science in an e-mail. Moreover, within the physique, different substances compete to bind to the identical blood group antigens, so it is unclear what number of coronavirus particles would finally latch on, he added.
What’s extra, the kind A antigens discovered on the floor of airway cells may also be secreted elsewhere within the physique, equivalent to within the saliva, he stated. Meaning the virus may probably bind to those free-floating antigens, as nicely, lowering the variety of viral particles that attain the respiratory cells, he stated.
And along with distinctive antigens, totally different blood varieties additionally carry particular blood group antibodies, molecules that assist the immune system remove international invaders, Barington stated. These antibodies are significantly “prevalent in blood group O people and have been proposed to neutralize virus on our mucosal surfaces,” he stated. It might be that each blood group antigens and antibodies affect the probability of COVID-19 an infection, and their particular person contributions will should be sorted out, he stated.
Regarding the new research, “it is an vital first step,” Stowell stated. “The vital factor to do [now] is to find out whether or not the precise virus, by way of its potential to contaminate cells, is influenced by blood group antigens or not.”