Most people don't know this –
Over 70% of your body's immune system is in your gut.
That's powerful information. Three systems provide the protection: physical, innate and adaptive.
The mucous layers on the walls of your digestive system offer a physical barrier to invaders. They keep pathogens from contacting the epithelial cells of your intestines, and from penetrating to enter your bloodstream. The mucosal lining also provides a welcome environment for your "good" probiotic bacteria's immune cells and for other beneficial molecules. Keeping your gut healthy supports optimal physical barrier protection.
But your gut offers other, even greater defenses.
This is key to know –
Your GI tract has your body's largest reserves of lymphoid tissue. This gut-associated lymphoid tissue, or GALT, stores your immune cells including B and T lymphocytes. These are part of your "innate" immune system. These immune cells defend against and attack pathogenic bacteria and toxins.
When pathogenic bacteria or toxins enter your body, your innate immune system recognizes them through "pattern recognition receptors." Your injured or infected cells respond with the release of leukotrienes, prostaglandins and cytokines, which then cause inflammation and increased blood flow to the area. This release also attracts white blood cells, called leukocytes.
These leukocytes recognize and attack pathogens by engulfing and ingesting them, or attaching them with digestive enzymes. One cytokine called "interferon", fights viruses by shutting down protein synthesis in the infected cell. And as chemical mediators, cytokines also attract beneficial immune cells to the sites of infection.
Your innate immune system activates white blood cells, which identify bad bacteria and foreign or toxic materials in your blood, lymph, tissues and organs. And through "antigen presentation" your innate immune system also signals and activates your "adaptive" immune system, so it can join in the fight.
Your adaptive immune system has a memory. That's why vaccines work. Once exposed to a specific pathogen, your adaptive immune system remembers it, allowing you to generate stronger responses each time the pathogen is encountered again. This is thought to occur through gene changes in your antigen receptors that affect your lymphocytes and their DNA. These changes are passed down to offspring of those cells, including Memory B cells and Memory T cells. It's part of what's called the immune network theory.
There you have it.
Three immune response systems: physical, innate and adaptive.
All highly integrated. All highly dependent upon a healthy gut.
If your gut is performing optimally, your immune systems can too.