However, a new study led by researchers from the University of Pennsylvania in the US has confirmed red blood cells also play a critical role in inflammation, one that could make a life-or-death difference.

As far back as the middle of last century scientists had their suspicions that red cells played some kind of role in keeping invaders at bay. By the 1990s, researchers were uncovering receptors on red blood cells that responded to inflammatory messenger chemicals called cytokines.

Initial tests on human and chimpanzee blood confirmed they also existed on red blood cells.

Thanks to their recent analysis of blood samples taken from sepsis and COVID-19 patients, the researchers now know that the number of receptors, specifically TLR9, increases during infections.

"Right now when patients in the ICU [intensive care unit] become anemic, which is almost all of our critically ill patients, the standard is to give them blood transfusions, which has long been known to be accompanied by a host of issues including acute lung injury and increased risk of death," says Mangalmurti.

"Now that we know more about the mechanism of anemia, it allows us to look at new therapies for treating acute inflammatory anemia without transfusions, such as blocking TLR9 on the red blood cells."