Why do people have different blood types?

More than a century after the discovery of blood types, people still do not really know our bodies split up different blood types to do? And does having such blood types really affect?

The Mosaic science website has published an article explaining the blood types of journalist Carl Zimmer so that we can understand the science of blood types.

1. When my parents told me my blood type was A, I felt a little strange pride. If A + is the best scale in school, surely A is also the best type of blood type.

40% of whites have type A.

But soon I realized it was stupid to feel that way. But I still don't know much about what type A blood really means. When I was an adult, all I knew was that if I had to go to the hospital and needed a blood transfusion, the doctors would have to know for sure that they needed to give me blood bags of the right blood type.

The lingering questions are still there. Why are 40% of white people with type A blood, when only 27% of Asians have this blood type? Where do the different blood types come from? And what do they mean? To get the answer, I met experts - doctors, geneticists, evolutionary biologists, virologists and nutrition scientists.

In 1900, Austrian physician Karl Landsteiner was the first to discover blood types, and won the Nobel Prize in Physiology and Medicine for this research in 1930. Since then scientists have developed a lot of Powerful tool to learn about blood types. They discovered some interesting clues - such as tracing the "ancestors" of blood types and finding the effects of blood types on human health. But in many ways, blood types remain a mystery. Scientists have yet to give a satisfactory explanation of the existence of blood types.

2. Today, doctors know about blood types, and they can save many lives by blood transfusion. But in history, the idea of ​​passing one person's blood to another was a dream. Renaissance doctors once thought about what would happen if they put blood into a patient's veins. Some argue that it could be a treatment for all sorts of illnesses, including insanity. Finally, in the 1600s, some doctors experimented with the idea, producing terrible results. A French doctor injected a calf's blood into a mentally ill man. The person immediately sweats, vomits, and the urine turns gray. After a blood transfusion, he died.

Such accidents make blood transfusions notorious for 150 years. Even in the 19th century, only a few doctors dared to conduct blood transfusions. One of them is an English doctor named James Blundell. Like other doctors, he witnessed many female patients die from bleeding during childbirth. After the death of a patient in 1817, he realized that it was impossible not to experiment with blood transfusion.

" I could not stand it any longer, the patient could have been saved if he had a blood transfusion, " he later wrote.

Dr. Blundell believes that previous blood transfusion disasters were caused by a very basic error: transfusion of "animal blood" . Therefore, he concluded that doctors should not exchange blood from one species to another , because " different types of blood differ greatly ".

That is, the patient should only accept human blood. But still no one has tried such a blood transfusion. And Blundell tested it by designing a system of funnels, tubes and syringes that could transfuse blood from a blood donor to a patient. After experimenting with this system on dogs, Blundell was put in a situation where he had to save a patient who was bleeding to death. " A blood transfusion alone can give him a chance to live ," he wrote.

And some blood donors gave Blundell 14 ounces (about 0.4 liters) of blood, which he injected into the patient's arm. After that process, the patient said he felt better - but 2 days later he died.

However, the experience convinced Blundell that blood transfusion would be of great benefit to humankind, and he continued to give blood to many desperate patients for many years to come. Reportedly, he performed 10 blood transfusions. 4 patients were saved.

3. Blundell is right in believing that humans should only accept human blood. But he didn't know another important fact about blood: that people should only accept blood from certain people . It may be a mistake that causes some patients to die. What made those deaths all the more tragic was the discovery of blood types, then a few decades later, as a result of a fairly simple procedure.

In the late 1800s, when scientists mixed the blood of many people in test tubes, they noticed that sometimes red blood cells were stuck together. But because this is often the blood of patients, they think such clots as well as some other type of pathology are not worth investigating. No one cares about the blood of healthy people, until Karl Landsteiner wonders what will happen. Immediately, he found that blood mixes of healthy people sometimes clotted.

Humans should only accept human blood.

Landsteiner makes a chart to track blood clotting . He took blood samples from everyone in the lab, including his blood. Each blood sample was split into two parts consisting of red blood cells and plasma (plasma), then he proceeded to mix one person's plasma with the red blood cells of another.

Landsteiner discovered that blood clots only if he mixes the blood of certain people together. By testing all the combinations in turn, he eventually sorted his blood types into three groups, according to the alphabet names A, B and C. (Later blood type C was renamed to O , and a few years later other researchers discovered the AB group. In the middle of the 20th century, American researcher Philip Levine found another way to classify blood, based on whether the blood type was weak. Rh factor or not, if any, it will be denoted Rh +, if not, write it Rh-, write next to the blood type names).

When Landsteiner mixed the blood of different people, he discovered a number of rules. If you mix the blood of a person with type A blood and red blood cells of another person of type A, the blood is still liquid, not clotted. The same thing happens with the blood of people of group B. But if you mix the blood of people with type A blood and people with type B blood, and vice versa, the blood will clot.

People with type O blood are different. If Landsteiner mixes blood type A and B blood with group O plasma, the blood clots, but if the group A and B plasma mixed with group O blood cells, the blood is still normal.

It is the clot that makes the blood transfusion potential . The clots interfere with blood flow and cause massive bleeding, difficulty breathing and possibly death. Landsteiner did not know exactly how to distinguish blood types. Later generations of doctors discovered that the red blood cells in each type of blood had different molecules on their surface. In blood type A, for example, cells build molecules in two stages, like two floors of a house. The first layer is called the H. antigen. On the surface of this first layer, the cells build a second layer, called the A. antigen.

Meanwhile, the blood of the B people built the second floor of the house in a different shape. And people with type O blood only have a one-story house: that is, the cells only build the H antigen layer and not build any more.

The immune system of people in the same group will have many similarities. If people were given the wrong type of blood, the immune system would react, as if the strange blood was an aggressor. This is the exception for people with type O blood. Type O blood has only the H antigen, and this antigen is included in the other blood types. Therefore, people with type O blood can transfuse blood with type A or B blood. This similarity makes people with type O blood become "valuable blood donors".

Landsteiner's findings opened a safe window for blood transfusions, even today blood banks still use his clot-like blood cell testing to test blood types. Fast, reliable.

But while Landsteiner answered the old question, he asked new questions. That is, the blood type to do? Why do people have different blood types?

4. In 1996, a natural therapist named Peter D'Adamo published the book "Eat Right 4 Your Type". D'Adamo thinks we have to eat according to our color group, to be in harmony with our evolution.

D'Adamo stated that blood types " seem to have reached an important crux of human evolution ". According to D'Adamo, blood type O comes from the ancestors of hunter-gatherers in Africa, blood type A is at the dawn of agriculture and blood type B from 10,000 to 15,000 years ago in the Himalayan highlands . Blood type AB is a modern combination of blood type A and B.

Blood type AB is a modern mix of blood type A and B.

From these assumptions, D'Adamo stated that blood type will determine what foods we should eat. For example, people with type A blood should be vegetarian. Ancient O blood hunters should have a diet high in meat and avoid grains and milk. According to the book, foods that are not suitable for blood types contain antigens that can cause all sorts of illness. D'Adamo recommends diet as a way to reduce infections, lose weight, fight cancer and diabetes, and slow down the aging process.

The book D'Adamo has sold 7 million copies and has been translated into 60 languages. Following D'Adamo's book, a series of books on diets suitable for blood types also appeared. D'Adamo also sells blood-styled diets on his website. As a result, patients often ask the doctor whether the blood type diet really works.

The best way to answer that question is to conduct a test. In Eat Right 4 Your Type, D'Adamo writes that he conducted a decade-long trial of blood type diets for women with cancer. However, 18 years later, data from this trial has not yet been released.

Recently, researchers at the Belgian Red Cross in Belgium decided to look at whether there is any beneficial evidence in a blood type diet. Despite testing more than 1,000 studies, it was useless. " There is no direct evidence that the health effects of blood type diets ," said Emmy De Buck of the Red Cross.

However, some people on the diet have had positive results. According to Ahmed El-Sohemy, a nutrition scientist at the University of Toronto, that is not a reason to think that blood type dieting is successful.

El-Sohemy is an emerging expert in nutrigenomics - a combination of nutrition and genes. He and his colleagues studied 1,500 people. As a scientist, he realized that Eat Right 4 Your Type is not scientific at all.

5. After Landsteiner discovered human blood types in 1900, scientists wondered if other animals had such blood types. It seems that some primates have blood mixed with human blood types. But for a long time, people did not know what the finding was for. In fact, a monkey's blood does not clot with blood type A, does not mean that the monkey has inherited the same gene type A.

Beginning in the 1990s, scientists deciphered the molecular biology of blood types. They discovered that there is a single gene, called ABO, that is responsible for building the second floor of the blood type home. The A gene version has a number of important mutations that are different from the B gene. People with type O blood have mutations in the ABO gene, making it impossible for them to form an enzyme that builds antigen A or B.

The scientists were then able to start comparing human ABO genes with other animals. Laure Ségurel and colleagues at the National Center for Scientific Research in Paris led an ambitious study of the ABO gene in primates. And they realized that human blood types actually originated very far back. Apes and humans have variants of both A and B blood types, and those variants come from a common ancestor, living 20 million years ago. Even human blood types have an older origin, it is difficult to know the age.

6. The most eloquent evidence of man's ignorance of the benefits of blood types came to light in 1952 in Bombay. Doctors discovered that a small number of patients had no ABO blood type - that is, no A, no B, no AB, no O. If blood types A and B were two-story houses, and blood type O was the for a one-story house, the blood of Bombay patients has only "a vacant lot".

"Bombay phenotype" also appears in some other people, but very rarely. And according to the scientists, it's not harmful. Its only risk is when a blood transfusion is needed. People with the Bombay phenotype can only accept blood from people in similar situations. Even blood type O, considered to be the most universal blood type, is not accepted.

Some scientists think the explanation for blood types may lie in variations in blood. That's because different blood types can protect us from various diseases.

The first time doctors realized a link between blood types and various diseases was in the mid-20th century. " There are still a lot of associations between blood types and infections, cancers and some diseases. " , Pamela Greenwell of Westminster University said. For example, people with type A blood have an increased risk of certain types of cancer, such as pancreatic cancer and blood cancer; Also prone to chicken pox, heart attack and malaria. On the other hand, people with type O blood can develop ulcers. According to the study, this is because immune cells, such as those with type O blood, are better able to identify infectious cells than other blood types.

What is more confusing is the relationship between blood types and diseases that have nothing to do with blood. For example, norovirus (Norovirus is the virus that causes diarrhea, vomiting and abdominal pain. Norovirus is often called by other names such as gastroenteritis, gastritis, and food poisoning). Norovirus spreads like a cruise ship, sweeping through hundreds of passengers, causing intense vomiting and diarrhea. It invades cells in the intestines, causing blood cells to be affected. However, blood types do influence the risk that they will be infected by a particular strain of norovirus.

The answer to this mystery may lie in the fact that blood cells are not the only cells that produce blood type antigens. These antigens are also produced by cells in the walls of blood vessels, airways, skin and hair. Many people even have their saliva secreting blood type antigens. Norovirus makes us sick by penetrating the blood group antigens produced by cells in the gut.

However, norovirus can only enter a cell if its proteins fit the antigen of the blood group. Therefore, it is possible that each norovirus strain has a protein that matches certain blood group antibodies. That explains why blood types can affect the type of norovirus that makes us sick.

This could be a clue to why a type of blood group has been around for millions of years. Our primate ancestors have to fight constantly with countless pathogens, including viruses, bacteria and other enemies. Some pathogens may have adapted and learned to exploit different types of blood type antigens.

Finally, author of science site Mosaicscience.com said the story of blood type made him wonder when he was a boy, and when he grew up, he realized: "Finally, reason because I have type A blood is also nothing! " It's just that my parents gave birth to me like that .

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