The connection between exercise and inflammation has interested researchers since a study showed a spike of white cells in the blood of Boston marathon runners following the race.

Now a new Harvard Medical School study, published in the journal Science Immunology, offers a molecular explanation, suggesting that the beneficial effects of exercise may be driven in part by the immune system.

Researchers found that inflammation in the muscle caused by exertion mobilises inflammation-countering T-cells (or Tregs), which not only reduce inflammation, but also enhance the muscles’ ability to use energy as fuel, improving overall exercise endurance.

The power of Tregs
Long known for their role in countering inflammation linked to autoimmune diseases, Tregs were identified by researchers as key players in the body’s immune responses during exercise.

“The immune system – the T-cells in particular – have a broad impact on tissue health that goes beyond protection against pathogens and controlling cancer,” said Diane Mathis, professor of immunology at Harvard Medical School. “Our study demonstrates that the immune system exerts powerful effects inside the muscle during exercise.”

The findings come amid intensifying efforts to understand the molecular underpinnings of exercise and untangling the immune system’s involvement in this process is one aspect of these research efforts.

“We’ve known for a long time that physical exertion causes inflammation, but we haven’t fully understood the immune processes involved,” said study first author Kent Langston, postdoctoral researcher in the Mathis lab. “Our study shows what T-cells do at the site where exercise occurs – in the muscle.”

Frequency of exercise
Treg activity had a positive impact on exercise-induced inflammation in cases of both regular and one-off exercise, however, the metabolic and performance benefits of this immune system response were observed only in the regular exercisers.

Sedentary subjects did not experience either benefit.

The study findings provide a glimpse into the cellular inner workings behind the anti-inflammatory effects of exercise and underscore its importance in harnessing the body’s immune defenses, researchers said.

“Our work suggests that with exercise, we have a natural way to boost the body’s immune responses to reduce inflammation,” Mathis said. “In this research, we only looked at its impact on the muscle, but it’s possible exercise is boosting Treg activity elsewhere in the body as well.”