GALT: Gut Associated Lymphatic Tissue

According to Elizabeth Lipski, current research indicates that 70 percent of the immune system is located in or around the digestive system. The mucosal surface of the gut is only one cell thick. Underneath this is the gut-associated lymphatic tissue (GALT). It must continually distin­guish between friend and foe in the foods we eat and in the gut bacteria. When the digestive system is presented with a foreign substance, an antigen, specialized cells called M-cells carry the antigen to the lining of the digestive tract. There they are checked out or sampled, by specialized cells called Peyer's patches in the intestinal lining. These cells in turn alert B- and T-cells to begin processing the antigens. The B- and T-cells carry the antigens back to the intestinal mucosa, where they are gobbled up by macrophages, part of the cell-mediated immune system.

When microbes enter the digestive system, they are confronted with several nonspecific and antigen-specific defense mechanisms including: peristalsis, bile secretion, hydrochloric acid, mucus, antibacterial peptides, and IgA. This stops most microbes and par­asites from infecting the body. Those that do get through this defense system are recognized by toll-like receptors (TLRs). When disease-causing microbes get through, the TLRs stimulate production of inflammatory cytokines by activation of NF-kappa B, triggering cytokine production and inflammation in the gut.

It is believed that the constant exposure to microbes in infancy and early childhood contributes to the health and responsiveness of the adult immune system. This theory is called the "Hygiene Hypothesis." In our culture, we don't challenge the immune sys­tem enough. We have improved sanitation, low bacterial avail­ability in the foods we eat because of preservatives and food processing, decreases in consumption of fermented foods, fewer childhood infections, increased use of antibiotics, and routine use of vaccinations. Children who have little challenge to microbes are at risk for allergy, eczema, and asthma, which may continue throughout a lifetime.

Serotonin is best known for its role in the brain, but 95 percent of our serotonin is manufactured in the gut. Without adequate amounts, we have insomnia and are depressed. Many selective serotonin reuptake inhibitor (SSRI) drugs are on the market to help keep serotonin in the synapses for a longer period of time. The most well-known of these is Prozac.