Mice Raised in a Germ-Free Environment Exhibit Less Age-Related Inflammation and Longer Average Lifespans April 14, 2017, 11:37

Researchers raised mice in a germ-free environment, and found that they did not suffer anywhere near the same age-related increase in inflammation, and the average life span increased. You might compare it with another recent study in which germ-free mice developed less metabolic waste in brain tissues over a lifetime. The research here focused on the interaction between gut microbiota and the immune system over the course of aging, a topic that has been explored to an increasing degree in recent years. The influence of the microbial populations of the gut on long-term health appears to be of around the same order of magnitude as that of other prominent environmental factors, such as level of exercise, though no-one has yet demonstrated as large an effect as that of calorie restriction via manipulation of gut microbes.

The high level summary is simple to outline, but the picture is a complicated one under the hood. Even given just the three broad categories of (a) immune cells, (b) gut microbes, and © pathogens — a dramatic oversimplification of the real picture — we can still argue about the direction of causation. Does exposure to pathogens cause malfunctions in the immune system, that in turn leads to changes in the gut microbe populations, that in turn feed back to cause further immune issues and other problems in intestinal function? Or are direct effects of pathogens on gut microbes more important? Or are other bodily systems involved in a significant way? There is much work yet to be accomplished in this part of the field. Further, the usual caveats apply here despite promising supporting evidence from other parts of the field: mice are not people, and the interactions with pathogens that are important over a mouse life span are unlikely to be the same as those that are most important over a human life span.

That said, there is a good deal of evidence for the aging of the immune system over a normal human life span to be accelerated by exposure to persistent pathogens like cytomegalovirus. An ever increasing fraction of immune cells are dedicated, uselessly, to this class of invader, while other activities are neglected. The immune system malfunctions in ways that promote ever greater inflammation, but with ever less of the usual benefits in terms of increased beneficial immune activity. Transient inflammation in younger people is useful, a necessary part of the way in which the immune system functions. Chronic inflammation in the old, on the other hand, is essentially a form of damage that contributes to the progression of many age-related diseases. Further, we can look at recent human history to see the effects of reduced exposure to infectious pathogens on long-term health and average lifespans. Older people in a given age group today are considerably less physically aged than was the case for that age group a century ago. Further again, there is a fair amount of research in shorter-lived species to suggest that declining intestinal function is an important component of degenerative aging. In flies, for example, it might be the most important component, though in mammals that is probably not the case. That decline is linked, separately, to immune function and the microbes of the gut.

Source: https://www.fightaging.org/archives/2017/04/mice-raised-in-a-germ-free-environment-exhibit-less-age-...