Blood cells unexpected source of new nerve cells in crayfish

A new study led by researchers at Uppsala University and Wellesley College, USA, demonstrates that the immune system in crayfish can produce cells with stem cell properties. These cells can then develop into new nerve cells in the adult animal. The findings were recently published in the journal Developmental Cell.

For years, researchers have tried to determine how nerve cells are produced and integrated into the brain throughout adult life. In a new study, a team of international scientists provides evidence that adult-born neurons in crayfish are derived from a special type of circulating blood cell produced by the immune system.

‘Our findings in crayfish indicate that the immune system is intimately tied to mechanisms of adult neurogenesis, suggesting a much closer relationship between the immune system and nervous system than has been previously appreciated’, says Dr Irene Söderhäll, Department of Organismal Biology, Uppsala University.

In many adult organisms, including humans, neurons in some parts of the brain are continually replenished. This process is critical for ongoing health, and dysfunctions in the production of new neurons may contribute to several neurological diseases, including clinical depression and some neurodegenerative disorders.

The researchers studied crayfish to understand how new neurons are formed in adult organisms. When they marked the cells of one crayfish and used this animal as a blood donor for transfusions into another crayfish, they found that the donor blood cells could generate neurons in the recipient.

‘These blood cells – called hemocytes – have functions similar to certain white blood cells in mammals and are produced by the immune system in a blood-forming organ that is functionally analogous to bone marrow’, explains Dr Beltz of Wellesley College, USA. ‘When these cells are released into the circulation, they are attracted to a specialized region in the brain where stem cells divide, and their descendants develop into functional neurons.’

The current work demonstrates that the immune system can produce cells with stem cell properties that can give rise to different types of cells, including both blood cells and nerve cells. The plasticity of these immune cells in producing neurons in adult animals raises the intriguing possibility of the presence of similar types of plasticity in other animals.

‘If further studies show a similar relationship between the immune system and the brain in mammals, the results could be developed into a new research area. Although there is a long way from crayfish to humans, we can often learn a lot from simpler organisms, and the findings could stimulate a new area of research into immune therapies to target neurological diseases’, says Dr Irene Söderhäll.