The hard-working red blood cells are just like you who work hard...

When it comes to red blood cells, readers will definitely think of oxygen transportation immediately.

Yes, the numerous red blood cells in our body have established a life channel for us to transport oxygen. However, do the numerous red blood cells in the body only participate in the respiratory function and transport oxygen to the body?

It turns out that this is not the case. In addition to oxygen transport, scientists have further studied red blood cells and found that they are also involved in the body's immune regulation. (Are you surprised? After all, red blood cells are not involved in the immune regulation that we learned in high school.)

The huge number of red blood cells in the body contribute to every aspect of our life activities. Next, let us learn more about these little heroes!

Red blood cells that transport oxygen

The blood flowing through our body contains plasma and blood cells, and the largest number of blood cells are our red blood cells.

Image source: search.creativecommons.org

When we describe the shape of red blood cells, we usually use the round cake shape with a depression in the middle (I believe everyone is already familiar with its shape, after all, we have come into contact with it a lot in high school biology...), this is the result of it abandoning the nucleus and numerous organelles in order to transport oxygen. It is this shape that allows room for hemoglobin in the red blood cells to maximize the binding of oxygen, but it is also because of the abandonment of the nucleus that the average lifespan of red blood cells is only about 120 days. It can be said that red blood cells risk their lives to transport oxygen!

Image source: hippopx

Why can red blood cells transport oxygen? Because of hemoglobin!

The oxygen obtained by the body through respiration is first dissolved in the lipids of the alveolar surfactant, and then dissolved in the plasma of the blood through the alveolar wall and the capillary wall around the alveoli. The oxygen in the plasma enters the red blood cells through free diffusion and combines with the hemoglobin in the red blood cells to form oxygenated hemoglobin, which is then transported to all parts of the body through the systemic circulation.

Hemoglobin, image source: search.creativecommons.org

When blood with high oxygen partial pressure flows through the capillaries between tissues, the oxygen in the blood quickly separates from hemoglobin, diffuses through the capillary walls into the tissue cells and is used.

This is the process of red blood cells transporting oxygen that is known to the public. As scientists have carried out a lot of work on red blood cells, another function of red blood cells has also been discovered, which is to participate in the body's immunity.

Red blood cells sacrifice their own warning

As early as 1930, scientist Duke discovered that trypanosomes can adhere to human red blood cells in the presence of antiserum, and that the adhesion ability of red blood cells of different people to trypanosomes varies.

In 1953, Nelson discovered that human red blood cells can bind to specifically conditioned Treponema pallidum and Pneumococcus. Based on this, it is speculated that there are immune adhesion receptors on the red blood cell membrane that can promote the phagocytosis of white blood cells (I believe everyone knows the role of white blood cells in the body's immunity, especially phagocytes...). In short, scientists at this time have already linked red blood cells with the body's immune regulation.

Image source: pexels

Based on this speculation, many scientists from different countries have conducted research on the role of red blood cells in the body's immunity.

The latest research found that red blood cells can bind to DNA fragments, thus playing an important role in the body's immune regulation. The research report was published in the heavyweight journal Science Translational Medicine on October 20 this year.

Image source: PubMed

Scientists have previously discovered that red blood cells can also participate in the body's immune regulation, but their specific regulatory mechanisms are not clear.

In this newly published study, scientists obtained red blood cells from patients with sepsis and novel coronavirus pneumonia and found that there is a protein called TLR9 (Toll-like receptor) on the surface of these patients' red blood cells. This protein can bind to free CG-rich DNA fragments, which generally come from bacteria, malarial parasites, or mitochondrial DNA released by other damaged cells.

When a patient is infected by bacteria or viruses, the bacterial DNA or mitochondrial DNA fragments released by damaged cells bind to TLR9 on the surface of red blood cells, causing the shape of red blood cells to change. (From the original round pancake shape with a depression in the middle to a fried egg with multiple bulging small bags...)

Changes in red blood cell morphology, image source: Science Translational Medicine

The change in the shape of red blood cells prompts TLR9 to bind to more DNA fragments, eventually making the red blood cells unrecognizable, like a small ball covered with pustules. It is this abnormal appearance that alerts the body and triggers an immune response.

The phagocytes come roaring in and while clearing out the pathogens, they also clear out the red blood cells that have bound to the DNA fragments. The red blood cells can be said to be protecting the body in a suicide way!

Macrophage, image source: search.creativecommons.org

Of course, the removal of red blood cells means that the number of red blood cells that can work normally in the body is greatly reduced, which explains why critically ill patients in intensive care units often experience symptoms of anemia.

By understanding this important function of red blood cells, we may be able to further study methods to combat acute inflammatory anemia, or look for the cause through clues provided by red blood cells.

Image source: Science Translational Medicine

How about the hard-working red blood cells in your body? Do you love them? Are they just like you who work hard?

END

Review expert: Wu Xinsheng, deputy chief physician of the Department of Gastroenterology, the 371st Hospital of the People’s Liberation Army.

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Editor/Heart and Paper