Did you pile on the pounds this Christmas? At least you can take some comfort in the fact that not all fat is bad. Evidence in mice and monkeys suggests it is important for storing important immune cells and may even make them more effective at fighting infection.
at the US National Institutes of Health and her team have found that a type of immune cell – called a memory T-cell – seems to be stored in the body fat of mice. These cells learn to fight infection. Once exposed to a pathogen, they mount a stronger response the next time they encounter it.
When the researchers infected mice with parasites or bacteria, they found that memory T-cells clustered densely in the animals’ body fat. Tests showed that these cells seemed to be more effective than those stored in other organs, being better at replicating and at releasing infection-fighting chemicals, for example.
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After exposing the mice to the same pathogens again, the memory T-cells stored in their fat were the fastest to respond.
Belkaid’s team found that monkeys also have plenty of memory T-cells in their body fat, and that these cells worked better than those from other organs.
“It means that fat tissue is not only a reservoir for memory cells, but those memory cells have enhanced function,” says Belkaid. “The tissue is like a magic potion that can optimally activate the T-cells.”
Fat transplant
In a further experiment, the team took body fat from mice that had been exposed to a pathogen, and implanted it in mice that had never been infected with it. When these mice were then exposed to the bacteria or parasite, the memory cells in the donated fat kicked into gear, giving them as much protection as if they had encountered the pathogen before.
“It is sufficient to provide good protection against an infection,” says Belkaid.
She thinks these memory T-cells are particularly powerful because they may be feeding on the energy-rich fat tissue they are stored in. “It has an enormous amount of nutrients,” she says.
The findings should change the way we think about fat, says at Columbia University, New York. “If you picked up a textbook, it would list the immune organs as the lymph nodes, thymus, but this study and others are changing that.” Fat should be considered an immune organ, too, he says.
Not all fat is good. When people become obese, the relationship between fat tissue and immune cells seems to change, leading to harmful inflammation. However, having some fat is very healthy, says Belkaid.
“I don’t think the small perturbations in fat we experience from having a bit too much goose at Christmas are going to affect our immune systems,” says Ferrante. “But one perhaps can take some solace in [the knowledge] that good things are going on in our fat while we’re eating.”
Belkaid is now looking for immune cells in biopsies of human fat tissue. If she finds them, she will try to discover what exactly the fat cells do to boost the power of these cells. She hopes this could lead to new ways to boost our body’s immune response to infections, cancer and vaccinations. “You could take immune cells from a person, make them more aggressive and more able to fight cancer, and then put them back,” she says.
Immunity
Read more: Fat is a beautiful organ
