Science

The mysterious origins of ABO blood groups

We are not the only primate species with ABO blood groups! By going back in time thanks to genetics, the anthropologist and geneticist Laure Ségurel and her colleagues deduced a probably common origin of ABO groups in all primates, more than 40 million years ago.

The ABO blood group system is characterized by sugars present on the surface of our red blood cells, as well as on other cells and in free circulation. Yes, we have to talk about the system, the blood group being the antigen (s) of the system that you have (A, B, AB or O for example). Sugar (or antigen) A makes you a blood group A individual, B gives you blood group B, and when you have both or neither you have group AB and O respectively. the first to be described, in 1901, but this is only one of 43 erythrocyte blood group systems, that is, present on our red blood cells – because other cells, like white blood cells, they too have their blood group systems.

The mysterious ABO system of humans

Humans are not the only ones who have the ABO system: other primates also have variations of ABO. Gorillas are for example all of group B, orangutans can be A, B or AB, and chimpanzees are all A or O. Humans seem to be distinguished from other primates by two characteristics.

First, it is the only one to have such a high rate of individuals from group O (more than 40% of O in France for example). Why ? Mystery! Then, 20% of us are “non-secreting”, that is to say that none of the ABO markers are found in our fluids such as saliva or sperm, nor on the respiratory and digestive cells. Yet this is the case for all other primates – and 80% of humans anyway!

Why this appearance of non-secretory profiles? For Laure Ségurel, anthropologist and geneticist, it may have to do with certain infections. “Non-secretors are immune to the gastroenteritis virus norovirus, which uses ABO antigens as a gateway. In these individuals, the virus therefore cannot enter the intestinal cells.“. The same goes for group O, which seems slightly protective for several infections, such as Covid-19.”Antigens are also expressed in respiratory tissue and are often entry points for viruses“, explains Laure Ségurel.”It is quite rare to see differences in blood groups associated with susceptibilities for viruses, hence the great interest in Covid-19!“This slight advantage of group O vis-à-vis certain infections could also explain its strong presence in humans, who from the time of sedentarization and the invention of agriculture had to coexist with cattle and increase the transmission of diseases. .

Viruses and bacteria would explain that none of the groups A, B, AB or O supplants the others

But if O is advantageous, why does the diversity of blood groups persist over time, without any – O for example – being imposed on a lasting basis? “This diversity is necessarily maintained for a good reason “, says Laure Ségurel. Here again, several hypotheses stand out. First, it could be that the different antigens are in turn more or less advantageous depending on the infections encountered. Group B, very present in Asia, seems for example a little more protective against cholera. It could also be that this diversity is cyclical: an emerging infection would be more likely to adapt to the majority form of blood group, giving others an advantage that will allow them to spread. This is a phenomenon called “advantage over the rare”. For Laure Ségurel, the first hypothesis is the most probable.

The ABO system does not come from red blood cells, but from the intestines

In truth, having sugars A or B on its red blood cells is a peculiarity of great apes, of which we are a part: other primates only have them on their epithelial tissues, in particular respiratory and intestinal tissues. “The evolution of the ABO system therefore probably has nothing to do with its expression on red blood cells and must have arisen from the expression on our epithelia. (tissues, editor’s note) “, deduces Laure Ségurel. In works of 2012 in which she participated, she compares two hypotheses which would explain the presence of the ABO system in all primates: either we all had a common ancestor who possessed this system on its tissues and transmitted it to us, or it appeared independently of each other in each species. The principle of parsimony would be that it is a common heritage dating from at least 40 million years ago“, in the common ancestor of primates, she concludes. The principle of parsimony, also called Ockham’s razor, wants in fact that of several hypotheses, we favor the simplest, that which requires the least actions and d successive events.

One thing is certain: the ABO system appeared over 20 million years ago, which is the time when hominids broke away from great apes. As to how many exactly… Impossible to know with genetics, says Laure Ségurel, because too many mutations have accumulated over time on the same portions of DNA, making the background noise too high. The method that will clarify this mystery therefore remains to be discovered.

Each blood group has its own diet: false!

According to the bestseller “4 blood groups 4 diets” by naturopath Peter d’Adamo, published at the end of the 1990s, each blood group should benefit from a specific diet. Group O, allegedly appeared among hunter-gatherers, should favor meat. Group A, supposed to date from the invention of agriculture, should instead eat cereals and milk, and group B from livestock, dairy products. As for the AB, the most recent of the four according to Adamo, it is entitled to more flexibility. “It’s attractive, it’s simple, we understand everything, but it’s wrong“, asserts Laure Ségurel. As seen previously, the ABO system probably already existed 40 million years ago, well before the birth of humanity! On the other hand, food may interact with blood group sugars. , present in the intestine … But that does not prevent you from eating balanced, quite simply.

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