Ask an Expert

Do primates have different or similar blood groups to humans?

Humans owe a lot to the Rhesus macaque.

This little monkey has provided insights into space travel, cloning and human behaviour.

But perhaps most importantly it first alerted scientists to the existence of the famous 'Rh factor' in human blood, a molecule that is either present (Rh+) or absent (Rh-) on our red blood cells, says Dr Bruce Rideout from San Diego Zoo's Institute for Conservation Research.

The 'Rh' stands for the rhesus monkey because researchers recognised that this human blood antigen was similar to a rhesus monkey blood antigen.

Blood types have only been studied in a handful of primate species, but Rideout says Old World monkeys and apes have been shown to have blood types comparable, although not identical, to the human ABO blood group system.

According to the Australian Red Cross there are more than 270 human blood antigens, belonging to over 30 blood group systems.

The two major blood group systems used in transfusions are the Rhesus factor and the ABO blood group system.

What blood type we have is determined by the molecules or antigens on the surface of our red blood cells.

For example in the ABO blood group system people with blood type A have one type of molecule, whereas people with blood type B have another. People with blood type AB have both molecules on their red blood cells and people with blood type O have no molecules of this group present.

These antigens also have corresponding antibodies in our blood plasma to identify when foreign antigens are introduced into our bodies.

People with blood type A have anti-B antibodies, blood type B have anti-A antibodies, blood type AB have neither antibody and blood type O have both.

Antigens and antibodies become very important in matching blood for transfusions.

"If you don't match the donor and recipient blood type, the immune system of the recipient will recognise the transfused blood as a foreign invader and will destroy all of the transfused blood cells," says Rideout.

"O-blood… can generally be transfused into any recipient because it lacks both the A and B molecules and the Rh factor, so there is nothing important on the surface of the transfused blood cells that the recipient immune system will recognise as foreign," says Rideout.

With proper cross-matching you could theoretically do transfusions between closely-related species, like apes and humans, says Rideout.

But there are enough differences between ape and human ABO systems that could influence the success of a xenotransfusion.

Rideout says these differences have occurred because once human ancestors and other primates became reproductively isolated from one another the genes that encode or regulate the presence of the molecules on the surface of red blood cells began to accumulate small mutations and drift away.

As the genetic mutations that occurred in one population didn't necessarily occur in the another, over time these changes have accumulated.

Even if we could overcome this evolutionary gap, most ape and primate species are either endangered or threatened.

So, with human blood supplies dwindling, some scientists have suggested humans may owe their lives to another mammal in the future: the pig.

But that's another story.

Dr Bruce Rideout was interviewed by Suzannah Lyons.