Immunity and red blood cells
Red blood cells activate innate immunity
Marina Astvatsaturyan, Echo of Moscow
Tens of trillions of human red blood cells circulating in his bloodstream may not only supply oxygen to tissues, but also perform an unexpected function for biologists: they scan the body for signs of infection or cell damage. A study published in the journal Science Translational Medicine (Lam et al., DNA binding to TLR9 expressed by red blood cells promotes innate immune activation and anemia) showed that red blood cells, erythrocytes, signal the immune system about the presence of bacteria, parasites, as well as extracellular mitochondrial DNA. All these are factors that mean a serious illness, such as sepsis or pneumonia. This role costs red blood cells, and the body is not cheap: cells that bind to DNA fragments die, and the consequence of this is anemia associated with inflammation.
According to The Scientist, when Nilam Mangalmurti, a resuscitator and researcher from the University of Pennsylvania, entered graduate school in 2005, she was interested in the question why transfusion of red blood cells can cause lung damage. In that study, the first evidence of the interaction of red blood cells with the immune system was found, but the data were obtained in the context of a red blood cell transfusion procedure.
However, over the past decade, Mangalmurti and colleagues and other groups of scientists have established that both transfusion, that is, transfused, and circulating red blood cells are not just containers for oxygen–carrying hemoglobin in the body, but cells with many functions unrelated to gas exchange. "Perhaps they have an effect on the immune response, which we have ignored all these years," says the researcher.
In 2018, her group showed that red blood cells use toll-like receptor 9 (TLR9), a sensory molecule that provides innate immunity, to bind extracellular mitochondrial DNA. With the help of a toll-like receptor 9, red blood cells cleanse the body of fragments of this already unnecessary genetic material.
High levels of free circulating mitochondrial DNA in the blood indicate disease or intense cell death. In a new study, the authors found that in patients with sepsis or malaria, the amount of toll-like receptor 9 on the surface of red blood cells is significantly increased compared to the level in healthy people.
Binding of free-floating DNA by the receptor leads to deformation of red blood cells, as a result of which they die, and anemia develops in the body, a lack of hemoglobin that carries oxygen.
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