A new study from researchers at the Babraham Institute in the UK suggests age-related immune system decline is not irreversible, and can possibly be improved by replenishing an aging gut microbiome. The scientists discovered fecal transplants from young mice to old mice resulted in significant improvements to the animal's gut immune system.

As we grow older, among the multitude of changes that occur in our bodies is a slow decline in the diversity of our microbiome. Several studies have chronicled clear differences between the microbiomes of older humans and those of younger adults. This new research set out to uncover whether these age-related microbiome changes were associated with decreases in gut immune function.

"Our gut microbiomes are made up of hundreds of different types of bacteria and these are essential to our health, playing a role in our metabolism, brain function and immune response," says Marisa Stebegg, lead researcher on the study. "Our immune system is constantly interacting with the bacteria in the gastrointestinal tract. As immunologists who study why our immune system doesn't work as well as we age, we were interested to explore whether the make-up of the gut microbiome might influence the strength of the gut immune response."

The study conducted fecal transplants designed to rejuvenate the microbiome of older mice with samples from its younger counterparts. The results were compelling, with the older mice showing distinct improvements in gut immune responses.

"To our surprise, co-housing rescued the reduced gut immune response in aged mice," says Michelle Linterman, leader of the Immunology program at the Babraham Institute. "Looking at the numbers of the immune cells involved, the aged mice possessed gut immune responses that were almost indistinguishable from those of the younger mice."

It's important to note that this study was only conducted in mice, and there is no suggestion the results would be similar in humans. So don't go hunting for that fecal fountain of youth just yet. However, the study does help indicate that the relationship between an aging gut microbiome and a weakened immune system may be somewhat causal. By confirming that a modification of the microbiome can result in improvements to immune system responses, the study adds to a slowly growing body of evidence implicating the gut in a variety of age-related conditions.

An intriguing 2017 study found when middle-aged killfish were administered fecal transplants from youthful fish they lived 37 percent longer than their untreated counterparts. A more recent mouse study discovered that modulating the microbiome of middle-aged mice improved immune functions in the brain, slowing general age-related cognitive decline. And, we also know that immune cells in the gut can directly be linked to neuroinflammation in the brain.

All this accumulating research is inarguably compelling but it certainly is still early days for the field. It may be some time before all these discoveries are effectively translated into clinical treatments, but it looks like in the future healthy aging may be facilitated by a variety of microbiome alternations.

The new study was published in the journal Nature Communications.