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Positive news about O-negative

The human body is a complex structure composed of organs, muscles, and fluids. The most important of the fluids is blood. It is a mixture of cells and plasma. A typical adult has around five litres flowing through their circulatory system.
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The human body is a complex structure composed of organs, muscles, and fluids. The most important of the fluids is blood.

It is a mixture of cells and plasma. A typical adult has around five litres flowing through their circulatory system.

The plasma makes up about 55 per cent of the fluid and is mostly water containing proteins, glucose, minerals, hormones, carbon dioxide and the various blood cells.

The blood cells can be divided into at least three distinct groups. Red blood cells dominate with somewhere close to five million per microliter of fluid (which translates to five trillion per liter).

Males have slightly higher levels and females slightly lower levels of red blood cells.

These cells, as their name suggests, give blood its distinctive hue. They contain the molecule hemoglobin which is composed of a protein wrapped around a heme prosthetic group. At the core of the heme is an iron atom coordinated by a porphyrin ring system.

It is the iron atom which picks up oxygen in the lungs and releases it in our tissues.

The red in red blood cells comes for the electronic structure of the iron when it is coordinated by oxygen so arterial blood appears quite red compared to venous blood.

However, venous blood still carries about 40 per cent of its oxygen load, so it takes on a purplish hue which results from a combination of the red oxygenate iron atoms and the blue deoxygenated iron atoms. It is the latter which give veins their distinctive colour below our skin.

Red blood cells lack a nucleus and many of the organelles found in other cells. This severely limits the lifespan of the cells to around 120 days and means we constantly need to be producing more. But the lack of DNA in red blood cells means they are not susceptible to attack by viruses or other pathogenic agents - they don't get sick.

Blood also contains platelets or thrombocytes which are critical to forming blood clots. They clump together at wounds and form a bridge of protein fibres which prevent further loss of blood. The mechanism is complex but is initiated by any injury to a blood vessel which is why clots sometimes form within our bodies.

The other major category of cells in our blood are the white blood cells. They are part of the body's immune system as they remove and destroy any old or aberrant cells and any cellular debris within the blood plasma. They also attack anything they do not recognize as being part of the self. That is, they will attack infectious agents such as pathogens but also any cell without the proper tagging.

Autoimmune diseases can occur when the immune system mistakes healthy cells for invaders. White blood cells are particularly susceptible to being attacked which leads to other diseases.

Beyond the general structure of our blood, things get a little more specific. Everyone generally has one of four blood types with type O being the most abundant at 45 per cent of the population. Type A (40 per cent), Type B (11 per cent) and Type AB (four per cent) are the other common types although there are a very small number of individuals who do not fit into these general categories.

An individual with Type A blood has a particular sugar on the surface of their red blood cells which can be detected by the immune system. If a person with Type A blood is given Type B instead, the immune system will recognize the cells as foreign and destroy them. Initially, this results in fever, chills, and bruising initially it can lead to a clotting cascade in which cell destruction blocks vital arteries.

In this case such an incompatibility could lead to stroke or a heart attack.

Medical personnel are keenly aware of this issue and if they do not know a person's blood type, they use Type O blood. The red blood cells lack both the A and B markers and, as a consequence, do not trigger a response.

Blood cells have another tag called the Rhesus factor which can be either present (positive) or not. If a person is given the wrong factor, the immune system will kick in again attacking the new cells.

As a consequence, people with an O-negative blood type are universal donors. However, they only make up seven per cent of the general population.

Earlier this month, Dr. Stephen Withers and colleagues at UBC presented a paper at the American Chemical Society detailing their work with a stomach enzyme capable of chewing off the Type A tags on red blood cells. Researchers have been studying enzymes for removing surface sugars from red blood cells since 1982, but Withers new enzyme is the most effective yet.

His work could allow any Rh-negative blood to be turned into O-negative, potentially increasing the supply of universal donors if it can be successfully transferred from the lab to production.