Recently, a group of scientists from the Karolinska Institute in Stockholm and other institutions began to wonder about white blood cells. As part of the immune system, white blood cells play a key role in fighting cancer by recognizing, navigating to, and often killing malignant cells. Researchers have known for some time that different types of immune cells tend to fight different types of cancer. However, little is known about whether and how exercise affects any of these immune cells, and whether these changes may contribute to the cancer-repelling effects of exercise.
For the new study, published in eLife in October, the Swedish scientists decided to learn more by inoculating mice with different types of cancer cells and letting some rodents walk while others remained sedentary. After a few weeks, the researchers found that some of the runners showed little sign of tumor growth. More interestingly, most of these active mice have been vaccinated with cancer cells, which are known to be particularly susceptible to a certain type of immune cell known as CD8 + T cells, which are primarily prone to certain forms of breast cancer and other solids to fight tumors.
Perhaps, the researchers speculated, exercise had particular effects on these immune cells.
To find out, they then chemically blocked the action of these T cells in animals that carried tumor cells and let them run. After a few weeks and despite being active, the animals with no functioning CD8 + T cells showed significant tumor growth, suggesting that CD8 + cells at work must be an integral part of how exercise contributes to some cancers fend off.
For further confirmation, the scientists then isolated CD8 + T cells from animals that had walked and those that had not. They then injected one type of T cell or the other into sedentary, cancer-prone animals. Animals that received immune cells from the runners then fought tumors significantly better than animals that received immune cells from inactive mice.
These results surprised and excited the researchers, says Randall Johnson, professor of molecular physiology with double appointments at the University of Cambridge in England and at the Karolinska Institute, who oversaw the new study. They seemed to show "that the effect of movement on T cells is intrinsic and persistent," he says.