Human body treated all of the food that we ate, either plants or animals, as foreign substances. It is body immune system’s function to protect us from foreign material’s intrusion which may causes harmful to us. Then why does our immune system not oppose and refuse foreign materials that we consume as food?”
Naturally, if our body totally reject those foods which get into our body, we could not survive! Then, what is it that allows for food to plainly evade the roadblock of immune cells and be taken up into our bodies? In the final process, food become an integral part of our tissues and organs, and then be used as fuel for essential body processes. Research has begun to reveal part of the answer to this important issue in our body complex immune system question: the complex series of events known as oral tolerance.
Digestive Tract’s Immune System
Part of overall body immune system, which is associated with digestive tract immune system is having different immune mechanism. Digestive Tract’s Immune System comprised of specialized function cells that make up Gut Associated Lymphoid Tissue (GALT). This system allows the processing of food through the uptake of nutrients by the walls of the digestive tract without triggering the protective reaction that would otherwise form a barrier to the foreign materials in food. Concurrently, whatever potentially disease-causing microorganisms taken in through the same route are effectively excluded by the GALT. At the same time and in the same place we have a system that can differentiate and recognize any foreign material that is safe (food) and foreign material that is a threat (microorganisms, toxins, and other noxious agents).
It is known that approximately 70% of the body’s immune system is found in the digestive tract. Gut Associated Lymphoid Tissue is consisted up of various types of lymphoid tissue that store immune cells, such as T and B lymphocytes. These cells carry out attacks and defend against pathogens. Latest research indicates that Gut Associated Lymphoid Tissue may continue to be a major site of HIV activity, even if drug treatment has reduced HIV count in the peripheral blood.
Microorganisms in the Large Intestine: The Resident Gut Microflora
In addition to separating between food and potential pathogens, Gut Associated Lymphoid Tissue must also distinguish between invading microorganisms and others that are permanent residents of the large intestine, called the gut microflora, or gut microbiota. It is estimated that there are about 1012–1014 fairly innocuous microorganisms per mL in the gastrointestinal tract of the healthy human, mostly in the large bowel. They crack-up the undigested food that gets into the bowel from the small intestine. Micronutrients such as vitamin K, vitamin B12, , thiamin, biotin, and folate are developed as a result of their gut microflora metabolic activities. We absorb these vitamins, and gut microflora or gut microbiota form an essential part of our nutritional resources.
The relationship between gut microflora and humans is not merely communal or a non-harmful coexistence, but rather is a mutuality, symbiotic relationship. Though people can survive with no gut microflora, the microorganisms perform a host of useful purposes, such as fermenting unused energy substrates, training the immune system, preventing growth of harmful species, regulating the development of the gut, producing vitamins for the host, and producing hormones to direct the host to store fats. However, in certain conditions, some species are thought to be capable of causing disease by causing infection or increasing cancer risk for the host.
In addition, microorganisms in the large bowel defend the bowel from invasion by nonessential, or frankly harmful, microorganisms by competing with them for space and nutrients. They also perform a vital role in keeping the surrounding tissues healthy by stimulating the GALT in a positive manner. Resident microorganisms playing probiotics’ role in digestive tract health.
The Process of Immunological Tolerance (Oral Tolerance) to Food in the Digestive Tract
As in all immunological responses, the process of oral tolerance involves T cells and their “messenger chemicals,” cytokines. As far as we know at present, in the normal healthy (non allergic) human, T cells that first encounter the “foreign food” when it enters the body for the very first time (perhaps in mother’s breast milk, or as a solid food after weaning) are of the Th1 type. The food molecules are picked up by special cells (usually dendritic cells) in the infant’s digestive tract. The antigenic parts of the food are then “presented” to the T cells where they couple with special receptor molecules on the T cell surface. The T cells with the attached food molecules are then transported in the lymphatic system to the thymus gland. In the thymus gland, the regulatory T cells (sometimes written as Treg cells) stop any further action on the part of the Th1 cells when it is discovered that the “foreign molecules” pose no threat to the body.
The “educated” T cells are then transported, in the blood circulatory system, back into the digestive tract GALT as “memory cells.” Whenever the same food is eaten again, the memory T cells remember that this material is safe and remain quiescent, without any further attempt to protect the body from this particular foreign material. As far as we know, this process occurs every time a new food enters the body for the first time.
