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Why we have different blood types and how they influence coronavirus infection

2020-07-27T11:13:13.197Z


People with type A blood may have an increased risk of contracting covid-19 and develop severe symptoms, new research suggests, while people with type O blood have ...


A + blood type would make you more prone to covid-19 1:17

(CNN) - Most humans belong to one of these four blood groups: A, B, AB, or O.

Normally, your blood type makes very little difference in daily life, except if you need a transfusion.

However, people with blood type A may have an increased risk of contracting covid-19 and develop severe symptoms, new research suggests, while people with type O blood have a lower risk. The results of this study follow the evidence from previous research that certain blood groups are more vulnerable to other diseases such as cancer.

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It is still largely unknown why we have different blood types and what purpose they serve, and very little is known about their links to viruses and diseases. Unlocking the role that blood types play could potentially help scientists better understand the risk of disease for people of different blood groups.

"I think it's fascinating, evolutionary history, although I don't think we have the answer as to why we have different blood types," said Laure Segurel, geneticist of human evolution and researcher at the National Museum of Natural History of France.

Why do they matter

Blood types were discovered in 1901 by Austrian immunologist and pathologist Dr. Karl Landsteiner, who later won a Nobel Prize for his work. Like other genetic traits, the blood type is inherited from the parents.

Before the discovery of blood groups, a transfusion, a common procedure that now saves lives, was a high-risk process. Pioneering physician James Blundell, who worked in London in the early 1800s, gave blood transfusions to 10 of his patients and only half survived.

What he didn't know is that humans should only obtain blood from certain other humans.

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Here's why: The ABO blood group system is identified by antibodies, part of the body's natural defense system, and antigens, a combination of sugars and proteins that cover the surface of red blood cells. Antibodies recognize any foreign antigen and tell your immune system to destroy it. That is why giving someone blood from the wrong group can be life threatening.

For example, I have type A + blood. If a doctor accidentally injected me with type B, my antibodies would reject it and work to break down foreign blood. As a result, my blood would clot, interrupt my circulation, causing bleeding and shortness of breath, and I would potentially die. But if I received type A or type O blood, it would be fine.

Your blood type is also determined by Rh status, an inherited protein found on the surface of red blood cells. If you have it, you are positive. If not, you are negative.

Most people are Rh positive, and can obtain blood from compatible blood types that are negative or positive. But people with Rh negative blood should normally only get Rh negative red blood cells (because their own antibodies can react with the blood cells from the incompatible donor).

That leaves us with eight possible primary blood types, although there are some more rare ones.

At the center of each figure are the donors and on the edges are the possible recipients. As we can see, type O negative blood can be used in transfusions to people with any type of blood.

Evolutionary puzzle

Not only humans have blood types, at least 17 different types of primates as well, including chimpanzees and gorillas. Evolutionary biologists have discovered that blood types are ancient, dating back 20 million years to a distant ancestor that we share with primates.

"Many species of primates ... also have the differences of being A, being B, being AB," said Segurel. "Whether it is a great ape or a new monkey, it is quite curious that differences have been found or maintained in so many different species," he added.

Blood types are unlikely to have lasted that long by chance. They must give us some kind of evolutionary advantage, Segurel said.

The ABO blood type gene not only influences our blood. It is also active in a wider variety of tissues and organs, including our digestive or respiratory systems, Segurel explained. This can be important when our bodies face infections with different blood types that offer us protection against different pathogens and diseases.

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"The evolutionary interest in maintaining these (blood) types may not be related to their function in the blood but to their function in the respiratory or digestive tissues," he said. "They are the two places where you have the most contact with viruses and bacteria: the places where air and digestive tissue are inhaled," he explained.

“If you imagine a cocktail of pathogens (…) there could be a cycle in which sometimes B is advantageous, and sometimes A is. If you go through those different preferences, you end up with a population with different blood types, ”he added.

While we don't know precisely how, Segurel said that variation in the blood type gene influences our susceptibility to different diseases. What we do know is that certain blood groups are more vulnerable to certain diseases.

For example, blood type B has been associated with a reduced risk of cancer, while group O has been associated with a lower risk of dying from severe malaria, but appears to be more susceptible to infection by norovirus, the winter vomit that also causes diarrhea.

And what about the coronavirus?

A handful of studies have shown a link between blood type and the new coronavirus, although most involved a small number of people, and some were not peer-reviewed.

A team of European researchers who published their findings in the New England Journal of Medicine in June found that people with type A blood had a 45% higher risk of infection than people with other blood types, and people with type O blood. they had a 65% chance of being infected than people with other blood types. They studied more than 1,900 severely ill coronavirus patients in Spain and Italy, and compared them to 2,300 people who were not sick.

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A similar effect was observed in Hong Kong healthcare workers with blood group O during the SARS outbreak, which infected 8,098 people from November 2002 to July 2003 and is from the same family of viruses.

There are two hypotheses about the link between blood groups and covid-19, said Jacques Le Pendu, director of research at Inserm, a French medical research organization. One is that people with type O are less prone to clotting problems, and clotting has been a major factor in the severity of covid-19 cases.

Le Pendu said it could also be explained by the probability that the virus carries antigen from the infected person's blood group. As such, antibodies produced by a person from blood group O can neutralize the virus when infected by a person from blood group A, similar to the rules for blood transfusions.

However, this protection mechanism would not work in all situations. A person from blood group O could infect another person from blood group O, for example, ”he explained, adding that any protective effect is unlikely to be large and that the amounts of antibodies are highly variable from person to person.

People with type A should not be alarmed and people with type O should not relax, said Sakthivel Vaiyapuri, associate professor of Cardiovascular Pharmacology at the University of Reading in the UK.

Vaiyapuri, in collaboration with Thi-Qar University in Iraq, is conducting a study on the role of blood types based on data from more than 4,000 people in Iraq who had covid-19 and 4,000 who did not get sick. He said that the first results suggest that type O could have a protective effect, but it is not definitive. And given the number of underlying variables that exist, any effect, protective or not, is likely to be quite small.

For example, the idea that having type O blood is protection does not match the pattern of covid-19 infections in the United States. Type O blood is more prevalent among black people, who have experienced disproportionately high infection rates.

“People in group O should not think that they are not going to get this disease. They shouldn't be running everywhere and not keep social distance, (as well as) group A shouldn't panic, ”he said.

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"There are so many underlying factors. We think of this as a respiratory virus, but it's actually a complete collection of things that are happening that we don't yet understand, ”he said.

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Blood type research has sometimes fallen into different academic disciplines, but a better understanding of why we have different blood groups and the relationship between blood type antibodies and disease risk will likely help us develop vaccines and design new drugs. , even for the covid-19.

Blood

Source: cnnespanol

All news articles on 2020-07-27

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