human stem cell
© Hal X. Nguyen and Aileen J. Anderson
A human stem cell replicating itself.
That scab that forms after you cut yourself is the work of your immune system coming to the rescue, fighting off invaders, and helping to heal the wound.

But when it comes to spinal cord injuries, the healing process goes awry.

Immune cells rush in and cause a scar that blocks the ability of neurons to regrow and reconnect. However, recent studies have shown that the immune system can also aid regeneration.

"The immune system has both positive and a negative impact - what it does is really context specific," says Jan Kaslin, who studies neural regeneration in zebrafish at the Australian Regenerative Institute of Medicine in Melbourne, Australia.

Stem cells provide a great hope for damaged spinal cords and brain injury - but it has not been clear on how the immune system may affect the regrowth.

Now a new study has taken a look at how stem cells and the immune system interact in the repair of the spinal cord. Led by Aileen Anderson from the University of California, Riverside and published in the Journal of Neuroscience, the study suggests that whether or not the immune system hinders or helps transplanted stem cells to regrow lost tissue may be influenced by the presence of certain kinds of immune cells.

The study used stem cells derived from human foetal brain tissue and transplanted them into mice with a wound in their spinal cord. They then blocked the invasion of a specific population of immune cells called neutrophils and observed how well the wound was repaired by transplanted the stem cells.

In contrast to earlier research, Anderson's team found with that with neutrophils out of the way the wound healed more easily, requiring few stem cells.

"This is the first data to show that the immune environment can be altered to allow stem cell populations to perform better in terms of restoring function," according to Anderson.

Can other immune cells be manipulated to increase the effectiveness of stem cell transplantation in spinal cord regeneration?

These findings "are an important of piece of the puzzle," says Kaslin, that "may significantly improve future stem cell transplantation approaches".