The hormonal and immune systems are the busy beavers of the body. The immune system is constantly checking every nook and cranny of the body for "bad stuff" and then getting rid of it. The hormonal system is constantly sending signals to body cells letting them know what needs to be done.
Carbon Dioxide is the Chief Hormone
Yale Professor Yandell Henderson once said that "Carbon dioxide is the chief hormone of the entire body; it is the only one produced by every tissue and that probably acts on every organ." Simply put, hormones count on carbon dioxide to do their job. The signaling of the pancreas is more efficient when carbon dioxide levels are higher in the body. Sex hormones that drive fertility are more effective when carbon dioxide levels in the body are higher.
Carbon Dioxide and the Immune System
As noted before, carbon dioxide plays the primary role in determining body pH. It's believed that many immune system problems are caused when the body's pH gets out of balance. A good example of this is allergies. When blood pH is off, the immune system's mast cells, the "bad stuff" hunters inside the body, become hyperactive and see innocuous, for most people, things like pollen and animal dander as a problem. In it's state of hyperactivity, the mast cell produces histamines that clog up your nose and make your eyes water to flush away and block the entry of more allergens.
Here in Central Oregon where I live, juniper pollen is a really big deal for many people. When these folks correct their breathing, more carbon dioxide is retained in the body, their blood pH normalizes and the allergic reactions are reduced or disappear. As a result, they get to spend more time playing outdoors in our natural beauty.
How we breathe and our ability to retain carbon dioxide in the body helps manage normal body pH. This in turn manages the sensitivities of the immune and hormonal systems, allowing them to function as expected. How we breathe really matters.