17/10/2020, 00h20, Photo: Reproduction.
Most human beings fall into one of these four blood groups: A, B, AB or O. Normally, your blood type makes little difference in your daily life, unless you need a blood transfusion. (read more below)
However, people with type A may have an increased risk of contracting Covid-19 and develop severe symptoms, as a recent study suggested, while people with type O blood have a lower risk. The results of this study accompany evidence from previous research that certain blood groups are more vulnerable to other diseases, including cancer.
However, there is still little information about why we have blood types and their purpose. Little is also known about the links they have with viruses and diseases. Unraveling the role of blood types could help scientists better understand the risk of disease for people in these different groups.
“I think evolutionary history is fascinating, even if I don’t have the answer to why we have different blood types,” said Laure Ségurel, geneticist and researcher at the National Museum of Natural History in France.
Why do they matter?
Blood types were discovered in 1901 by Austrian immunologist and pathologist Karl Landsteiner, who later won a Nobel Prize for Medicine for his work. Like other genetic characteristics, the blood type is inherited from the parents.
Before the discovery of blood groups, a blood transfusion (now a common life-saving procedure) was a high-risk process. Medical pioneer, physician James Blundell, who worked in London in the early 1800s, had blood transfusions in ten of his patients. Only half survived.
He did not know, among other things, that humans should only obtain blood from other human beings.
Here’s why: your ABO blood group is identified by antibodies (part of the body’s natural defense system) and antigens (a combination of sugars and proteins that line the surface of red blood cells).
The antibodies recognize any foreign antigen and tell the immune system to destroy it. That’s why giving blood to someone in the wrong group can be fatal.
For example, if a person has type A + blood and a doctor accidentally injects type B, the antibodies rejected it and worked to destroy the foreign blood. As a result, blood clots, interrupting circulation and causing bleeding and breathing difficulties – the likely result is death. But if you get type A or O blood, that’s fine.
Blood type is also determined by Rh status, an inherited protein found on the surface of red blood cells. If the person does, it is positive. If not, it is negative.
Most people are Rh positive, and they can receive blood from negative or positive matches. But people with Rh negative blood should normally only receive Rh negative red blood cells (because their own antibodies can react with incompatible donor blood cells).
As a result, there are eight possible primary blood types, although there are some rarer ones.
It’s not just humans who have blood types – at least 17 different types of primates do, too, including chimpanzees and gorillas. Evolutionary biologists have discovered that blood types are very old, having arisen 20 million years ago.
“Many primate species also have the differences of being A, B and AB,” said Ségurel. “It is quite intriguing that the differences have been found or maintained in so many different species, whether in a hominid or a platyrrhino (primates of the American continent).”
Blood types are unlikely to have lasted that long by chance. According to the French geneticist, they must give some sort of evolutionary advantage.
The ABO blood type gene does not only influence blood – it is also active in a wider variety of tissues and organs, including the digestive or respiratory systems. This can be important when the body faces infections with different blood types, offering protection for different pathogens and diseases.
“The evolutionary interest in maintaining these types (blood) may not be related to their function in the blood, but probably to their function in the respiratory or digestive tissues,” explained Ségurel. “These are the two places that you have the most contact with viruses and bacteria, the one through which you inhale air and digestive tissue,” she said.
“Now imagine a cocktail of pathogens. There may be a cycle in which B is advantageous; in others, A. Following these different preferences, the pathogen appears in a population with different blood types. ”
Although it is not known exactly how, the variation in the blood type gene influences susceptibility to different diseases. What is known for certain is that some blood groups are more vulnerable to certain diseases.
Blood type B, for example, has been linked to a reduced risk of cancer. In turn, group O was associated with a lower risk of death from severe malaria, but greater susceptibility to infection by norovirus, a pathogen that attacks in winter and causes gastroenteritis.
And the new coronavirus?
A number of studies have shown a link between the blood type and the new coronavirus, although most have involved a small number of individuals and some have not been peer-reviewed.
A team of European researchers who published the findings in the New England Journal of Medicine in June found that people with type A blood had a 45% higher risk of becoming infected than people with other blood types.
Those with type O blood had a 35% lower risk of being infected compared to other blood types. In that study, 1,900 patients with the new coronavirus in serious condition in Spain and Italy were evaluated, compared with 2,300 people who were not sick.
A similar effect was found among Hong Kong healthcare workers with blood group O seen during the outbreak of Severe Acute Respiratory Syndrome (SARS), caused by a virus from the coronavirus family that infected 8,098 people from November 2002 to July 2003.
There are two hypotheses about the link between blood groups and Covid-19, according to Jacques Le Pendu, research director at Inserm, a French medical research organization. One is that people with type O are less prone to clotting problems, and this has been a major factor in the severity of Covid-19.
For Le Pendu, this can also be explained by the probability that the virus contains the antigen of the infected person’s blood group. The antibodies produced by a person with blood type O can neutralize the virus when contracted from someone with blood type A, in an effect similar to the rules for blood transfusions.
“However, this protection mechanism would not work in all situations. A person in blood group O can infect another person in group O, for example, ”explained Le Pendu, adding that any protective effect is unlikely to be large and that the amount of antibodies is highly variable from person to person.
For the doctor Sakthivel Vaiyapuri, individuals with type A should not be alarmed, nor people with type O, relax. He is an associate professor of Cardiovascular and Poison Pharmacology at the University of Reading, UK.
In collaboration with Thi-Qar University in Iraq, he 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. The doctor said that the first results suggest that type O may have a protective effect, but that it is not definitive. Furthermore, considering how many underlying variables there are, any effect, whether protective or not, is likely to be very small.
The idea, for example, that having type O blood is protective does not match the pattern of Covid-19 infection in the United States. Type O blood is more prevalent among African Americans, yet they have had disproportionately high infection rates.
“People in group O should not think that they are not going to get this disease. They need to maintain social distance, they should not go around, and individuals in group A should not fear “, he advised.
“There are many underlying factors. We think of it as a respiratory virus, but there is indeed a whole set of things going on that we still don’t understand, ”he said.
Blood type research sometimes occurs across different academic disciplines, but a better understanding of why there are different blood groups, and the relationship between blood type antibodies and the risk of disease is likely to help develop vaccines and design new drugs, including for Covid-19.
Source: CNN Brasil