Many people don’t realize it, but our immune system has a vital role in healing ankle sprains and other muscle injuries.

In fact, injured muscles send out signals to the immune system that attract white blood cells to the damaged tissue. Some of these white blood cells, called macrophages, cause swelling but also remove debris from the injury site and prompt stem cells to coordinate regrowth of muscle tissue. However, as we get older, the immune cells involved in this process can’t stimulate muscle repair as effectively as they did when we were younger.

But a new study suggests that transplanting healthy immune cells can sped the recovery of muscles in older mice following two weeks of physical inactivity. The finding could eventually lead to the development of treatments that accelerate muscle repair and help older people recover from falls and other injuries as quickly as younger individuals.

In a series of experiments, researchers from University of Utah Health and Miami University in Oxford, Ohio, weakened muscles in young and old laboratory mice. These mice were then given a dose of macrophages taken from a set of young and old mice that were allowed to move freely around. Another set of mice with restricted movement were given saline treatment as a control.

The researchers found the experimental young mice that received immune cells from other young mice showed no difference in their muscle recovery compared to the control group. However, the older experimental mice, when given immune cells from younger mice, had improved muscle strength recovery to virtually the same levels as older mice that remained physically active.

In contrast, when younger experimental mice received immune cells from older mice, their muscles became weaker, suggesting that the old immune cells were somewhat dysfunctional. Interestingly, when older mice were given old donor immune cells, their muscle strength dramatically improved during recovery, he says.

The researchers theorize that even though the old immune cells are a bit less effective than young immune cells, they still have the potential to make a difference, particularly if enough of them are introduced to the muscle.