Old Friends Alliance
We all have microbial friends with which we form a life-long health alliance. They exist almost everywhere on and in the human body. They are clustered around the barriers of our bodies (gut, skin, lungs, urinary tract), reinforcing these boundaries, the good guys out-competing the bad guys, bacteria promote healing; in the vagina they guard against unwanted yeast; and in the mouth they break down food and protect teeth and gums. But that is just the tip of the iceberg. There is possibly no organ system in our body that the microbiota isn't connected with (gut-brain axis, gut-muscle connection, even gut-gonad axis) and we are starting to find bacteria in places we never expected (placenta, brain, eyes). No single part of our bodies is sterile, with microbes making up to 2kg of our body weight.
Our sanitised modern lives mean that our immune systems come into contact with certain microbes less often or later in life than before. The modern immune system's training and development is stymied by the gradual absence of its customary microbial targets. With nothing constructive to do, this leaves it crazily spinning its wheels. The result? Soaring rates of childhood allergies and autoimmunity, even heart disease and cancer.
Everything we look at is covered in microbes - we just can't see them. And 99% of them won't hurt us. The immune system is like an athlete: to become strong and adept, it needs training and practice, and these 'good' germs are its friends and coaches.
'Have your 'Old Friends' got your back?
The biggest microbial load, the gut, sits at the core of it all, connected to and influencing everything else, not least our immunity. It's a familiar fact (and yes, it's true) - indeed almost 70% of the entire immune system resides in the gut. Throughout life, we are constantly throwing all sorts of potentially problematic things into our mouths. The essential task of the gut immune system is to maintain a balance between immune reaction and tolerance. It is essential that this tolerance - called oral tolerance - is established from a young age.
Our immunity is about more than the genes we are born with. Responding to, learning from and and adapting to our environment, it is evolving from the moment we are born. And it does not evolve in isolation. Much of this environmental interaction is conducted by the rich and dynamic ecosystem of microbes that live on us, in us and around us - collectively known as our microbiota. Yes, we are superorganisms.
Based on current estimates, every one of us is home to a community of 38 trillion microbes - our microbiota - accounting for half of each of us (by cell count). Much as we fear germs, the bugs comprising our microbiota are actually our biggest health allies. Our lifelong task of trying to balance our immunity means relying heavily on certain exposures to good germs for proper calibration.
Our immunity developed through times of great peril, interacting with germs of all kinds - good and bad. When operating optimally, this immune-microbial alliance creates a dialogue that underpins our immunity, selecting, activating and terminating many of its various components as we need them, helping us distinguish self from non-self, danger from non-threatening. It determines how susceptible we are to infections and our likelihood of getting an autoimmune disease. This dialogue even controls how our brains function.