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A new study in the journal Science Advances provides evidence for a possible link between muscle mass and the health of the immune system, indicating that more muscle-bound people may be better equipped to fight off infections. According to the paper, muscle tissue acts as a kind of refuge for immune cells, where they can take shelter and avoid getting burnt out by the constant battle against invading pathogens.
Researchers have known for some time that T-cells – which identify and kill viruses and harmful bacteria – become exhausted when faced with chronic infections, resulting in a loss of function and a weakened immune response. This is often accompanied by a physical wasting away known as cachexia, which generally involves weight loss and a decrease in muscle mass.
The study authors therefore decided to investigate whether or not there is a link between T-cell function and skeletal muscle. To do so, they infected mice with a virus known as lymphocytic choriomeningitis virus (LCMV) and found that this caused the rodents’ muscles to release an increased amount of a signaling protein called interleukin-15 (IL-15).
This, in turn, helped to support the presence of muscle-infiltrating lymphocytes (MILs), which are undifferentiated immune cells that contain high levels of T-cell factor 1 (Tcf1), meaning they have a strong ability to develop into T-cells and to proliferate.
An increase in IL-15 after infection caused more MILs to migrate into the muscle tissue, where they entered pockets that were free of inflammation. As T-cells outside of these muscles became exhausted by continual activity and exposure to inflammation, these MILs were then able to rush into these infected regions and replenish them by differentiating into new T-cells.
“If the T-cells, which actively fight the infection, lose their full functionality through continuous stimulation, the precursor cells can migrate from the muscles and develop into functional T-cells,” explained study author Jingxia Wu in a statement. “This enables the immune system to fight the virus continuously over a long period.”
Taking their investigation a step further, the researchers then repeated the experiment using mice that had been genetically modified to develop more muscle. Once infected with LCMV, these muscly mice released even more IL-15 than their less brawny counterparts, and subsequently exhibited a stronger anti-viral response, with more T-cell activity. In other words, beefier mice proved better at overcoming the infection.
While the findings of this study don’t necessarily mean that burly humans have more immunity than those with less muscle, it does point to a need for more research into the link between physique and the immune system.
